Effects of a defender on run-up velocity and ball speed when crossing a football.

This study evaluated effects of defensive pressure on running velocity in footballers during the approach to kick a stationary football. Approach velocity and ball speed/accuracy data were recorded from eight football youth academy participants (15.25, SD=0.46 yrs). Participants were required to run to a football to cross it to a receiver to score against a goal-keeper. Defensive pressure was manipulated across three counterbalanced conditions: defender-absent (DA); defender-far (DF) and defender-near (DN). Pass accuracy (percentages of a total of 32 trials with 95% confidence limits in parenthesis) did not significantly reduce under changing defensive pressure: DA, 78% (55-100%); DF, 78% (61-96%); DN, 59% (40-79%). Ball speed (m · s(-1)) significantly reduced as defensive pressure was included and increased: DA, 23.10 (22.38-23.83); DF, 20.40 (19.69-21.11); DN, 19.22 (18.51-19.93). When defensive pressure was introduced, average running velocity of attackers did not change significantly: DA versus DF (m · s(-1)), 5.40 (5.30-5.51) versus 5.41 (5.34-5.48). Scaling defender starting positions closer to the start position of the attacker (DN) significantly increased average running velocity relative to the DA and DF conditions, 5.60 (5.50-5.71). In the final approach footfalls, all conditions significantly differed: DA, 5.69 (5.35-6.03); DF, 6 .22 (5.93-6.50); DN, 6.52 (6.23-6.80). Data suggested that approach velocity is constrained by both presence and initial distance of the defender during task performance. Implications are that the expression of kicking behaviour is specific to a performance context and some movement regulation features will not emerge unless a defender is present as a task constraint in practice.