Flag errors in soccer games: the flash-lag effect brought to real life.

In soccer games, an attacking player is said to be in an offside position if he or she is closer to the opponents' goal line than both the ball and the second-to-last defender. It is an offence for the attacker to be in an offside position and in active play at the moment a fellow team member plays the ball. Assistant referees often make mistakes when judging an offside offence, probably because of optical errors arising from the viewing angle adopted by them (Oudejans, Verheijen, Bakker, Gerrits, Steinbrückner, Beek, 2000 Nature 404 33). Looking more closely at Oudejans et al's data, we show evidence that the flash-lag effect may contribute significantly to these mistakes. Participation of the flash-lag effect in assistant referees' misjudgments would take this perceptual phenomenon from laboratory setups to a real-life situation for the first time.