Judging where a ball will go: the case of curved free kicks in football
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This study examined whether adding spin to a ball in the free kick situation in football affects a professional footballer’s perception of the ball’s future arrival position. Using a virtual reality set-up, participants observed the flight paths of aerodynamically realistic free kicks with (±600 rpm) and without sidespin. With the viewpoint being fixed in the centre of the goal, participants had to judge whether the ball would have ended up in the goal or not. Results show that trajectories influenced by the Magnus force caused by sidespin gave rise to a significant shift in the percentage of goal responses. The resulting acceleration that causes the ball to continually change its heading direction as the trajectory unfolds does not seem to be taken into account by the participants when making goal judgments. We conclude that the visual system is not attuned to such accelerated motion, which may explain why goalkeepers appear to misjudge the future arrival point of such curved free kicks.
KeywordsFlight Path Lateral Acceleration Magnus Force Ball Trajectory Interceptive Action
The authors would like to thank the players and coaches from Olympique de Marseille, AC Milan, Schalke 04 and Bayer Leverkusen who participated in this study; Adidas-Salamon Germany who facilitated contact with the clubs, and staff at Milan Lab, Milanello, Italy. The authors also thank Cédric Goulon and Florian Laborde for their assistance in creating the virtual environment.
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