Variability in tactical behavior of futsal teams from different categories.

The aim of the present study was to analyze the time series of team spread during futsal official matches in the frequency domain for different categories. Using an automatic tracking method, trajectories of 258 players (excluding goalkeepers) were obtained, composed of 79 players from the under-15 (U15) category, 86 from the under-18 (U18), and 93 from the professional. We calculated the team spread defined as the Euclidean norm of the distance-between-player vector as a function of time. We applied the Fast Fourier Transformation method and calculated the median frequency for each time series of spread. The results of mean ± SD of the median frequency of the time series of spread from the first to the second half were significantly different only for the U15 category (first half, 1.04 ± 0.46, second half 1.40 ± 0.34). The frequency values differed significantly between the categories. The younger categories presented a higher frequency of spread oscillation than the professional category, which reflects the dynamics of the game between attack and defense sequences. The results provide insights into the features of the sport and present a basis for appropriate training interventions for players in each category, planning for future transition to the following category.

Introduction

The futsal like other team sports have interpersonal interactions between teammates and opponent players. The teammates interact cooperating with each other on tactical strategies to achieve offensive and defensive success [1]. One of the objectives in the analysis of a sport is to develop methodologies to understand the physical, technical, and tactical characteristics during official matches and training sessions [2], aiding comprehension about the tactical actions performed by the players, interaction with the opponents, or recommendations established by the coaches during a match or training [3,4]. The organization of the players on the court may reflect the strategic actions and information about these tactical behaviors can be obtained by the quantification of the team surface area and spread [2].

A new technique used for tactical analysis in team sports is to understand the variability of time series in the frequency domain, related to the distribution of players in the field during a soccer match (such as team surface area, spread). For any signal represented by a time series, it is possible to perform spectral analysis, showing the distribution of the fluctuation intensity of a signal in the frequency domain [5,6]. Variability in the time series of spread (a measure of distances between teammates) during a match reflects the speed with which players increase and decrease team compactness during attacking and defensive activities during a match [5]. For soccer, a previous study [5] reported a decrease in the frequency of this signal from the first to the second half of the match. This decrease may be related to the physical performance of the players during the match, since the distances covered and percentage of distances traveled at medium and high speed also decrease during matches in both football and futsal [7-10]. Additionally, oscillation seems to correspond to the frequency with which the teams exchange ball possession [5].

In recent years, studies have been carried out to understand the tactical organization of futsal players, interpersonal coordination, and spatial-temporal dynamics in official matches or in training sessions [11-15], as well as studies that try to understand if tactical variables can present differences according to different categories in futsal [16,17]. Generally, these studies focused on variables that provide information about relative space and dispersion covered by the futsal players on the court. However, tactical performance is also dependent on how fast the player and teammates are able to organize themselves on the court when ball possession exchange occurs [5]. Additionally, it is possible that younger players, due to their lower tactical capacity [18], will not be able to maintain possession of the ball for long periods, which may showed a higher variability of the team spread, result in lower proficiency to maintain possession of the ball. Thus, the variability analysis of the spread of futsal teams from different age groups allows characterization of the profile of the game dynamics for categories that are in the process of learning of the sport modality as well as professional category.

The aim of the present study was to analyze the time series of team spread during futsal official matches in the frequency domain for different categories. This study presents two hypotheses: a) the younger the category, the greater the oscillation frequencies of the time series of spread would be, and b) these frequencies would decrease from the first to the second period, regardless of the category.

Materials and methods

Participants and match sample

The Research Ethics Committee of the University approved this study (process number. 22514). For this study, the Ethics Committee considered that an informed consent form signed by the participants or guardians was not necessary. The study was conducted between 2014 and 2016.

We registered images of fifteen matches for the present study, of these 5 matches for each category. The U15 (n = 79 players, regional championship), U18 (n = 86 players, state championship) and professional category (n = 93 players, professional championship) were the groups analysis. All matches were recorded in the State of Paraná –Brazil during the qualifying phase of the championships for all categories (Maximum score difference for each category: U15 = 5 goals; U18 = 3 goals; Professional = 5 goals). The recording method employed up to three cameras at a sampling frequency of 30 Hz, fixed in high points of the gyms, each one covering up to one third of the court, with regions of overlap between them. After the matches, we transferred the images to computers and synchronized the cameras by identifying common events that occurred in these regions of overlap, such as the exact moment of a kick.

Data collection

Was used an automatic tracking system to obtain the trajectory of each player via DVideo software [19,20]. For each match, we obtained a set of specific points, associated with the actual coordinate system of the court, and also determined the corresponding projection of these points in the image in DVideo software. The homography parameters of the image-object transformation were calculated based on the DLT (Direct Linear Transformation), providing the 2D coordinates of each player associated with the coordinate system of the court. The average error for the determination of player position was 0.098 m, and the average error for the distance covered was 0.8% [9].

Each player, from each team was numbered as p = 1, 2, …, 12. Thus, we defined the two-dimensional coordinates of the players as p (Xp(t), Yp(t)), where t represents each time instant (in seconds). Next, we used a 3rd order low pass Butterworth digital filter with a cutoff frequency of 0.4 Hz to smooth the 2D coordinate data of all players. Having obtained the smoothed trajectories of all players in each match, we calculated team spread as a function of time. Additionally, we identified which teams had and did not have possession of the ball according to the criteria defined by Moura et al, [5]

Data analysis

For each time instant t, we calculated the Euclidean distances of each player and their teammates. The distances between players were organized in symmetric matrix D of order m x n, where m = number of distance values between the players of the same team and n = corresponding frames to each time instant t [5,16]. The Euclidian Norm of each vector of the matrix D was then calculated, corresponding to spread values at each t, according to the equation:

Where p represents the number of players on the court of the same team and d represents the values of Euclidian distance between each pair of players from the same team. Larger ||D|| values mean that players are more spread across the court. In contrast, lower values indicate that players present a more compact structure [5,16].

For any time series, it is possible to identify the distribution of the fluctuation intensities of the signals in the frequency domain using spectral analysis [6]. We used FFT (Fast Fourier Transformation) in the Matlab® environment to calculate the power distribution in the frequency domain of the spread and the ball possession time series. Subsequently, we identified the median frequency, defined as the frequency dividing the integral of the power spectrum into two equal parts. In order to facilitate understanding of the results, the unit of measure adopted for the frequency was cycles.min-1.

Statistical analysis

Prior to each analysis, we performed a Levene’s variance test to verify the homoscedasticity of the data. As not all the tests met the assumptions, we performed a Box-Cox transformation to reduce data anomalies and heteroscedasticity. We used a two-way analysis of variance to verify if there were differences between the median frequencies of the time series of spread from the first to the second half (factor 1) and to verify if there were differences between the U15, U18, and professional categories (factor 2). In both analyzes, when differences were found, we performed a Tukey post-hoc test as a significant difference criterion. The significance level for all analyses was p<0.05. Data are expressed as mean and standard deviation. The effect size (EF) for the variance analysis was calculated according to Cohen’s f [21].

Specifically, we analyzed the time series associated with possession of the ball for each match in a descriptive way, calculating the percentages of changes in the frequencies, from the first to the second half in all the matches.

Results

Fig 1 presents examples of the time series of spread of the teams in the U15 (A), U18 (B), and professional (C) categories. Visual analysis of the time series between the teams demonstrated more oscillations of the time series of spread in the younger categories.

Fig 1

Time series of spread of different teams analyzed for the U15 (A), U18 (B), and professional (C) categories during ten minutes of the match.

Fig 2 exemplifies the results of spectral analysis of the first and second halves for the U15 (A), U18 (B), and professional (C) categories. These results represent the frequencies of the oscillations of the time series spread.

Fig 2

Examples power spectrum of spread as a function of frequency during the 1st and 2nd halves of play for the U15 (A), U18 (B), and professional (C) categories.

Table 1 presents the values of the median frequencies of the time series of spread of each team in the first and second halves for each category. Fig 3 presents the mean and standard deviation values for the median frequencies of spread found for each category in the first and second halves. Statistical tests revealed that the median frequency differed between all categories (F(2,60) = 28.1, p <0.01, ES = 1.50). When we analyzed all values from the first to the second half, the tests did not demonstrate statistical differences (F(1,60) = 0.23; p = 0.63, ES = 0.21). However, observing the interaction results, we verified that there were differences (F(2,60) = 8.15; p< 0.01, ES = 0.74). The post-hoc test showed that, during the matches of the U15 category, the median frequency values of the time series of spread increased significantly from the first to the second half (Fig 3).

Table 1

Median frequency values (cycles.min-1) for the time series of spread during the first and second halves of each team in every match analyzed for the U15, U18, and professional categories, and percentage change.

		Median Frequency (cycles.min-1)
Matches	Teams	U15			U18			Professional
		First Half	Second Half	Percentage Change (%)	First Half	Second Half	Percentage Change (%)	First Half	Second Half	Percentage Change (%)
Match 1	Team 1	1.75	1.61	-8.00	0.82	0.93	13.41	0.62	0.59	-4.83
	Team 2	1.96	1.98	1.02	0.88	1.06	20.45	0.53	0.64	20.75
Match 2	Team 3	1.14	1.44	26.31	0.77	0.94	22.07	0.75	0.41	-45.33
	Team 4	0.96	1.68	75.00	0.63	0.94	49.20	0.75	0.50	-33.33
Match 3	Team 5	0.65	1.09	67.69	0.75	0.55	-26.66	0.61	0.75	22.95
	Team 6	0.51	1.14	123.52	0.49	0.55	12.24	0.51	0.75	47.05
Match 4	Team 7	0.91	0.93	2.19	0.85	0.70	-17.64	0.67	0.85	26.86
	Team 8	0.81	1.35	66.66	0.64	0.65	1.56	0.45	0.56	24.44
Match 5	Team 9	0.85	1.05	23.52	0.76	0.61	-19.73	0.42	0.50	19.04
	Team 10	0.90	1.70	88.88	0.47	0.40	-14.89	0.23	0.48	108.69

Fig 3

Mean and standard deviation values of the median frequency of the time series of spread in futsal matches in the first and second halves for the U15, U18, and professional categories.

*p < 0.05; significant difference from the first to the second half, #p <0.05; significantly different from the professional category, †p < 0.05; significantly different from the U18 category.

Fig 4 shows the median frequencies found for the time series associated with possession of the ball in the first and second halves for each match in the respective categories; each line represents a match for the categories. The exploratory analysis enabled verification that, for the U15 category, the exchange of ball possession increased in the majority of matches analyzed, from the first to the second half in 4 matches. For the U18 category, there was a drop in the frequency of possession of the ball for the majority of matches, observed in 3 matches. In the professional category, there was also a drop in the median frequency in 3 matches. It was possible to verify a greater frequency for the youngest teams for the majority of matches.

Fig 4

Changes in the median frequency values (cycles.min-1) for the time series of ball possession of the first and second halves of each team in every match analyzed for the U15, U18, and professional categories.

Discussion

The aim of the present study was to analyze the time series of team spread during futsal official matches in the frequency domain for different categories. The main results of the present study demonstrated that, in general, the spread dynamics change in futsal matches of different categories. Our first hypothesis (a) was that the younger the category, the higher the variability of the team spread would be. We confirmed this hypothesis according to the quantitative data presented in Table 1. The results indicated that the dispersion movement of the players on the court in younger categories is higher in comparison to older players, reaching values of almost two cycles.min-1. In other words, younger teams have a tactical characteristic of spreading and compacting faster than the older categories, such as the U18 and professional. Higher frequency values for the U15 category may also be related to the magnitude of the spread values throughout the match, as seen in an example of the time series in Fig 1(A). Through visual analysis, it was possible to identify that the magnitude (i.e., the values range) of the spread values for matches in the U15 category was smaller compared to the U18 and professional categories (Fig 1(B) and 1(C), respectively). A recent study provided results that futsal players in the youngest categories present lower distribution values (surface area and spread) when compared to professionals [16]. We believe that these values could directly influence the frequency values, since if athletes spread less on the court when they are in possession of the ball, when they lose possession they compact faster, resulting in higher frequencies [5]. In another study, the authors point out that futsal is a complex sport, consider that the behavior of teams and players changes, vary, adapt on the court to obtain better organization and maintain the ball possession [22]. This may indicate that futsal is a sport that requires the learning of several tasks, therefore, teams of younger categories must improve performance in specific tactical tasks and obtain the ball possession for a longer time.

Another explanation may be related to the time which teams remain in possession of the ball. For this study, we analyzed the median frequency of ball possession exchange for all matches. These values of ball possession frequency could help in understanding the different game dynamics [5] and, specifically for this study, in different categories (Fig 4). An exploratory analysis showed that the youngest teams presented higher values in relation to the older teams, i.e. the U15 changes ball possession between teams faster than the other categories. The U18 category was slower in relation to the U15 and faster in relation to the professional. Since this outcome may represent the speed with which players spread and compact or vice versa, this could reflect behavior changes in the transition from attack to defense and vice-versa [5], but also this dynamic can be related to higher and lower levels of experience and learning [23]. Thus, these results suggest that the dynamics of the team spread, also for futsal, could be related to the capacity of maintenance of ball possession.

The literature reports that the distances covered by players in futsal matches decrease from the first to the second period [7,9]. Therefore, the second hypothesis raised was that players would present reduced frequency values during the second half due to the decline in physical performance. From the results found in the present study, it was not possible to confirm the second hypothesis (b), since only the U15 category presented changes in the frequency values, and the values increased in the second period. There were no significant frequency changes from the first to the second period for the U18 or professional categories. Although the literature reports a decline in physical performance for professional futsal players from the first to the second half, due to the unlimited substitutions allowed by the futsal laws of the game [9], it is probable that the teams were able to maintain tactical performance throughout the match.

Particularly for the results of the U15 category, the game dynamics increased during the match, observed by the power spectrum of the first and second halves (Fig 2(A)). Again, analyzing the frequency results for the time series related to ball possession of the matches (Fig 4), values increased in the majority of matches from the first to second half. Thus, the U15 presented decreased permanence of ball possession throughout the match.

The results found in the present study could help to provide better understanding of the behavior of players' dynamics in relation to the speed with which they expand and compact during a match, reflecting the interaction between attack and defense. Coaches should be attentive to the different behavioral changes in game dynamics in each category, and adequately train their athletes who are in the transition phase so that they can adapt to the different dynamics inherent to the following categories. Furthermore, higher team spread variability associated with a higher frequency of the ball possession may reflect the team's inefficiency in maintaining ball possession, this suggests the need for coach intervention during the match or in training planning.

The limitations of the study are mainly related to data acquisition. In this study we used a video-based system to acquire player’s positioning data and then calculate the analyzed variables. This method presents great accuracy and low-cost for its application [9], however, the system demands a great deal of time for image processing, which makes it difficult to collect data. Even so, as far as we know, this is the largest sample of futsal games ever reported in the literature.

Conclusions

Based on the results of the present study we concluded that younger categories demonstrate higher spread variability than professionals, which reflects the dynamics of play between attack and defense. However, the study repudiated the hypothesis that the speed of spreading and compacting actions would decrease from the first to the second half, as the U15 category demonstrated an increase in the game dynamics.

4 Dec 2019

PONE-D-19-25055

Variability in tactical behavior of futsal teams from different categories.

PLOS ONE

Dear Mr Bueno,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

We would appreciate receiving your revised manuscript by Jan 18 2020 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. This file should be uploaded as separate file and labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Filipe Manuel Clemente, PhD

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at http://www.journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and http://www.journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. We note that you have stated that you will provide repository information for your data at acceptance. Should your manuscript be accepted for publication, we will hold it until you provide the relevant accession numbers or DOIs necessary to access your data. If you wish to make changes to your Data Availability statement, please describe these changes in your cover letter and we will update your Data Availability statement to reflect the information you provide.

3. Please state in your methods section when you conducted this study.

4. Please include in your financial disclosure statement the name of the funders of this study (as well as grant numbers if available). At present, this information is only available in your acknowledgement section.

5. Please provide additional details regarding participant consent. In the ethics statement in the Methods and online submission information, please ensure that you have specified (1) whether consent was informed and (2) what type you obtained (for instance, written or verbal, and if verbal, how it was documented and witnessed). If your study included minors, state whether you obtained consent from parents or guardians. If the need for consent was waived by the ethics committee, please include this information.

6. PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager. Please see the following video for instructions on linking an ORCID iD to your Editorial Manager account: https://www.youtube.com/watch?v=_xcclfuvtxQ

Additional Editor Comments (if provided):

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The main idea of the manuscript is interesting and add to previous research. However, we consdier that the paper should be improved regarding the theoretical approach that sustains the main idea, the methods and the variables used. It was not clear the link between concepts such as tactical behaviour, variability, team spread, players' age and categories.

Please add a first general paragraph introducing the futsal as a team sport that requires tactical behaviours. Also there is a need to improve the link between tactical behaviour and variability.

L55 - distribution of players in the field?

L76-78 - The issue of variability in differnt players age should be improved. There are previous studies that reported variability as a measure of adaptability while other reported variability as a measure of low proficiency. The authors should improve the explanation and clearly define and justify their position.

L78-81 - players' age and players' experience are similar concepts?

L95-96 - Please describe each group in analysis instead of the category and the championship separatedly.

L120 - Why the authors used the described method to evaluate the pread of players in the court instead of convhull, strectch index or area of play.

L157-158 - Add during the text upper or lower pannel according to the description.

Reagrding the spectral analysis teh authors could choose to present the mean results on the text and maintain the figure or the opposite. It is not necessary to present the figure and the table. The information is redundant.

Add the values of effect sizes between the 1st and 2nd half of the match in Table 1.

It is not clear how the ball possession time-series was compared with the values of frequency of spread.

A theoretical justification is required to improve the discussion of results. The authors only described the results and add some perspectives without a clear discusssion based on scientific evidences. Please improve it.

Also, there is a need to present at the end of the manuscript the practical implications of the results for match analysis and training. The results means that worst teams tend to present high levels of variability in tspread than the best ones? What this imply?

Reviewer #2: The present study aimed to analyze the time series of tactical behavior of futsal players from different categories, in the frequency domain, using an automatic tracking method. The topic is within the scope of the journal and deals with a relevant topic. The authors arrive at the conclusion that younger categories demonstrate higher tactical variability than professionals, which reflects the dynamics of play between attack and defense. Although the paper is already in a good shape, I have some concerns with regard to this paper, which need to be appropriately addressed prior to publication of this manuscript in its present form in Plos One.

Major comments

- In my opinion, the main concern refers to the real meaning of the dependent variable analyzed (i.e., team spread). Does this variable really represent the tactical behavior of the team? I think that tactical behavior is broader than simply team spread. Perhaps the team spread is a "portion" of tactical behavior. Also, does higher spread dynamics really represent greater tactical variability? This term (i.e., tactical variability) is too broad. Finally, is higher dynamic spread good or bad to players performance? It is confusing what the practical significance of this measure really is.

- It may be interesting in this study to compare the spread dynamics according to the match status in the different categories (i.e., losing vs. drawing vs. winning). This would possibly help the auhors to better explain their results, rather than just characterizing the behavior of these variables across categories.

Specific comments

- I am not a English native speaker, but I suggest a language correction.

- The aims of "abstract", introduction "and" discussion "are not in line. In my opinion, the best aim of this study is exposed in the discussion: "The aim of the present study was to analyze the time series of team spread during futsal official matches in the frequency domain for different categories.”.

- I suggest separating the “Materials and Methods” section information into subtopics (e.g., participants and match sample, design, data collection, statistical analysis).

- Please, describe in more details the contextual factors of the matches analysed (e.g., location, quality of opponents, outcome/status, team formation, playing time – see previous recommendation). These variables may influence your findings.

- Maybe match status explains the results from comparing first vs. second period.

- Figures are fuzzies and will need to be improved/changed during the review process.

- Why the Figure 1 shows only 10 minutes of the matches?

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

22 Jan 2020

Responses to the reviewers

After incorporating the recommendations of the Academic Editor, we are resubmitting the paper “Variability in tactical behavior of futsal teams from different categories” for evaluation. We have addressed all the points raised in the review and are thankful for the editor and reviewers’ suggestions, which contributed positively to the quality of the study.

As recommended by the Academic Editor, the manuscript has been completely reformatted according to the PLOS ONE templates. We tracked all the changes in our manuscript and have added point-by-point responses to the reviewers’ comments as follows:

Academic Editor:

a) Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at http://www.journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and http://www.journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Thanks for the comments. We checked all the text and corrected if necessary.

b) We note that you have stated that you will provide repository information for your data at acceptance. Should your manuscript be accepted for publication, we will hold it until you provide the relevant accession numbers or DOIs necessary to access your data. If you wish to make changes to your Data Availability statement, please describe these changes in your cover letter and we will update your Data Availability statement to reflect the information you provide.

Dear editor, we added the data to the repository with the following DOI: http://doi.org/10.6084/m9.figshare.9772559.v1

c) Please state in your methods section when you conducted this study.

Thanks for the suggestion. We added in the corresponding session the period of the study.

d) Please include in your financial disclosure statement the name of the funders of this study (as well as grant numbers if available). At present, this information is only available in your acknowledgement section.

This information was added in the last session of “Manuscript Data” on the website for resubmission

e) Please provide additional details regarding participant consent. In the ethics statement in the Methods and online submission information, please ensure that you have specified (1) whether consent was informed and (2) what type you obtained (for instance, written or verbal, and if verbal, how it was documented and witnessed). If your study included minors, state whether you obtained consent from parents or guardians. If the need for consent was waived by the ethics committee, please include this information.

Thank you for this concern. The consent form was waived by the ethics committee, this information is added to the materials and methods session.

f) PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager. Please see the following video for instructions on linking an ORCID iD to your Editorial Manager account: https://www.youtube.com/watch?v=_xcclfuvtxQ

This information has been added.

Reviewer #1:

a) The main idea of the manuscript is interesting and add to previous research. However, we consdier that the paper should be improved regarding the theoretical approach that sustains the main idea, the methods and the variables used. It was not clear the link between concepts such as tactical behaviour, variability, team spread, players' age and categories.

We appreciate the reviewer's comments and suggestions. We have addressed all the points raised by the reviewer, as follows, in point-by-point responses.

b) Please add a first general paragraph introducing the futsal as a team sport that requires tactical behaviours. Also there is a need to improve the link between tactical behaviour and variability.

The suggestion was adopted, and we reformulated the first paragraph. The link between tactical behavior and variability has also been improved.

c) L55 - distribution of players in the field?

This sentence has been reformulated.

d) L76-78 - The issue of variability in differnt players age should be improved. There are previous studies that reported variability as a measure of adaptability while other reported variability as a measure of low proficiency. The authors should improve the explanation and clearly define and justify their position.

We agree with you and the paragraph was reformulated according to suggestion.

e) L78-81 - players' age and players' experience are similar concepts?

Thank you for this concern. The sentence was reformulated.

f) L95-96 - Please describe each group in analysis instead of the category and the championship separatedly.

The correction was performed.

g) L120 - Why the authors used the described method to evaluate the pread of players in the court instead of convhull, strectch index or area of play.

We use the team spread variable for tactical analysis because it has greater robustness. It considers the distance of each player to all his teammates, so the positioning of a player has less influence on the metric compared to the convhull or strectch index.

h) L157-158 - Add during the text upper or lower pannel according to the description.

The organization of the description and figures was reformulated.

i) Reagrding the spectral analysis teh authors could choose to present the mean results on the text and maintain the figure or the opposite. It is not necessary to present the figure and the table. The information is redundant.

Dear reviewer, the results presented in Table 1 correspond to the median frequency values for each team and the corresponding halves, separately, as well as the percentage change between periods for each team. The fig. 3 presents the mean and standard deviation of the results found in the study in relation to the median frequency values of the spread of the futsal teams, as well as the results of statistical differences between the periods and categories. Fig. 4 presents individual values of median frequency results for possession ball of all teams in the first and second halves.

j) Add the values of effect sizes between the 1st and 2nd half of the match in Table 1.

Dear reviewer, the results presented in Table 1 correspond to the median frequency values for each team and the corresponding halves, separately, as well as the percentage change between periods for each team. The effect size values are presented in the text when we applied statistical tests for comparisons between the halves or categories.

k) It is not clear how the ball possession time-series was compared with the values of frequency of spread.

We analyze the variability of the ball possession as a complement to the understanding of the game dynamics. A greater variability in team spread can be explained by higher frequencies of the ball possession change, but no comparisons were made between them.

l) A theoretical justification is required to improve the discussion of results. The authors only described the results and add some perspectives without a clear discusssion based on scientific evidences. Please improve it.

Thank you for this suggestion. We improved the discussion section based on theoretical foundations.

m) Also, there is a need to present at the end of the manuscript the practical implications of the results for match analysis and training. The results means that worst teams tend to present high levels of variability in tspread than the best ones? What this imply?

Thank you, this suggestion was adopted, and practical implications were inserted in the discussion section.

Reviewer #2:

a) The present study aimed to analyze the time series of tactical behavior of futsal players from different categories, in the frequency domain, using an automatic tracking method. The topic is within the scope of the journal and deals with a relevant topic. The authors arrive at the conclusion that younger categories demonstrate higher tactical variability than professionals, which reflects the dynamics of play between attack and defense. Although the paper is already in a good shape, I have some concerns with regard to this paper, which need to be appropriately addressed prior to publication of this manuscript in its present form in Plos One.

We appreciate the reviewer's comments and suggestions. We have addressed all the points raised by the reviewer, as follows, in point-by-point responses.

Major comments

b) In my opinion, the main concern refers to the real meaning of the dependent variable analyzed (i.e., team spread). Does this variable really represent the tactical behavior of the team? I think that tactical behavior is broader than simply team spread. Perhaps the team spread is a "portion" of tactical behavior. Also, does higher spread dynamics really represent greater tactical variability? This term (i.e., tactical variability) is too broad. Finally, is higher dynamic spread good or bad to players performance? It is confusing what the practical significance of this measure really is.

Thank you for this concern. We agree with you that the team spread variable does not represent the entire tactical behavior, but it provides information about him. The terminology has been reformulated throughout the text. This term was also changed in the title. We cannot establish that the greatest variability of team spread is bad or good, only when it is associated with greater variability of ball possession.

c) It may be interesting in this study to compare the spread dynamics according to the match status in the different categories (i.e., losing vs. drawing vs. winning). This would possibly help the auhors to better explain their results, rather than just characterizing the behavior of these variables across categories.

Thank you for your comments, even the acquisition system has a high accuracy to determine the position of the players, the system demands a great deal of time for image processing. This imply a low number of games to be analyzed which was not favorable to obtain an adequate number of information under the conditions losing vs. drawing vs. winning. We believe that in future studies this methodology can be applied and thus a better understanding of the modality.

Specific comments:

d) I am not a English native speaker, but I suggest a language correction.

The mistakes have been corrected. The manuscript was submitted to a native English review. Please find attached the certificate.

e) The aims of "abstract", introduction "and" discussion "are not in line. In my opinion, the best aim of this study is exposed in the discussion: "The aim of the present study was to analyze the time series of team spread during futsal official matches in the frequency domain for different categories.”.

Thank you for this concern. We corrected the aim of the study in the abstract and introduction sections.

f) I suggest separating the “Materials and Methods” section information into subtopics (e.g., participants and match sample, design, data collection, statistical analysis).

We adopted your suggestion and the materials and methods section was reformulated.

g) Please, describe in more details the contextual factors of the matches analysed (e.g., location, quality of opponents, outcome/status, team formation, playing time – see previous recommendation). These variables may influence your findings.

We didn't get some information, which may be one of the limitations of the studies because we don't have access to the player and coaches. We only had access with the coordinators and directors of the championships to obtain an authorization for the filming.

h) Maybe match status explains the results from comparing first vs. second period.

Thank you for your comments, even the acquisition system has a high accuracy to determine the position of the players, the system demands a great deal of time for image processing. This imply a low number of games to be analyzed. With a greater number of games, we believe that in future studies this methodology can be applied for a better understanding of the related to match results.

i) Figures are fuzzies and will need to be improved/changed during the review process.

The fig. 1 presents examples of the time series of spread for 10 min of first halve in the U15, U18 and Professional categories. The fig. 2, exemplifies the spectral analyzes for the time series of spread, being presented for a team of each category in the first and second halve. The fig. 3 presents the mean and standard deviation of the results found in the study in relation to the median frequency values of the spread of the futsal teams, as well as the results of statistical differences between the periods and categories. Fig. 4 presents individual values of median frequency results for possession ball of all teams in the first and second halves.

If you have any questions about the figures, please, let us know that we will certainly change them to the final version.

j) Why the Figure 1 shows only 10 minutes of the matches?

We chose to represent only 10 minutes of the matches to improve the visualization of the oscillations on the spread time series for all categories. Again, if you have any questions about the figures, please, let us know that we will certainly change them to the final version.

We would like to thank the reviewers and editor for their contributions and suggestions, which contributed positively to the quality of the study. We hope that the revision of our manuscript meets the publication standards of PLOS ONE.

The authors.

Submitted filename: Response to the Reviewers.docx

Click here for additional data file.

27 Feb 2020

PONE-D-19-25055R1

Variability in tactical behavior of futsal teams from different categories.

PLOS ONE

Dear Mr Bueno,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please consider the final minor corrections recommended by the reviewers

We would appreciate receiving your revised manuscript by Apr 12 2020 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. This file should be uploaded as separate file and labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Filipe Manuel Clemente, PhD

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: All comments of the Academic Editor and Reviewers have been addressed. Therefore, I accept the manuscript in the current form.

Reviewer #3: The article “Variability in tactical behavior of futsal teams from different categories” has a very relevant theme and I consider it to be appropriate to the scope of the PLos One. The variables of tactical behaviors in Futsal need further studies.

A suggestion for better clarity of the work and possible discussions about the athletes' tactical behaviors, would it be to put more information about the registered games, for example, were they games of the qualifying or final phase championship? Was it necessary to win to continue in the championship? We have observed that the tactical behavior of some athletes changes according to the difficulty or value of the game played. I think it would be interesting to make this information about games clear at work, even for new questions in the future.

In my opinion, after making such additions to the information in the description of the sample used, the work will be ready for publication, since the placements of the other reviewers were relevant and met by the vast majority of authors. I agree with all the other reviewers' comments, and since they were reviewed by the authors, I will not post again.

Congratulation for their work!

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: Yes: Rodrigo Aquino

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

28 Feb 2020

Responses to the reviewers

After incorporating the recommendations of the Academic Editor, we are resubmitting the paper “Variability in tactical behavior of futsal teams from different categories” for evaluation. We have addressed all the points raised in the review and are thankful for the editor and reviewers’ suggestions, which contributed positively to the quality of the study.

We tracked all the changes in our manuscript and have added point-by-point responses to the reviewers’ comments as follows:

Reviewer #2:

a) All comments of the Academic Editor and Reviewers have been addressed. Therefore, I accept the manuscript in the current form.

Thank you for the reviewer’s suggestions, which contributed positively to the quality of the study.

Reviewer #3:

a) The article “Variability in tactical behavior of futsal teams from different categories” has a very relevant theme and I consider it to be appropriate to the scope of the Plos One. The variables of tactical behaviors in Futsal need further studies.

We appreciate the reviewer's comments and suggestions. We have addressed all the points raised by the reviewer, as follows, in point-by-point responses.

b) A suggestion for better clarity of the work and possible discussions about the athletes' tactical behaviors, would it be to put more information about the registered games, for example, were they games of the qualifying or final phase championship? Was it necessary to win to continue in the championship? We have observed that the tactical behavior of some athletes changes according to the difficulty or value of the game played. I think it would be interesting to make this information about games clear at work, even for new questions in the future.

Thank you for this suggestion. We added detailed information to the corresponding paragraph.

We would like to thank the reviewers and editor for their contributions and suggestions, which contributed positively to the quality of the study. We hope that the revision of our manuscript meets the publication standards of PLOS ONE.

The authors.

Submitted filename: Response to the Reviewers.docx

Click here for additional data file.

3 Mar 2020

Variability in tactical behavior of futsal teams from different categories.

PONE-D-19-25055R2

Dear Dr. Bueno,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

Shortly after the formal acceptance letter is sent, an invoice for payment will follow. To ensure an efficient production and billing process, please log into Editorial Manager at https://www.editorialmanager.com/pone/, click the "Update My Information" link at the top of the page, and update your user information. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, you must inform our press team as soon as possible and no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

With kind regards,

Filipe Manuel Clemente, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

5 Mar 2020

PONE-D-19-25055R2

Variability in tactical behavior of futsal teams from different categories.

Dear Dr. Bueno:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

For any other questions or concerns, please email plosone@plos.org.

Thank you for submitting your work to PLOS ONE.

With kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Filipe Manuel Clemente

Academic Editor

PLOS ONE