A biomechanical analysis of the knuckling shot in football
Several studies on the non-spinning knuckleball have measured the steady aerodynamic forces in a wind tunnel (Carré et al., 2004) and have investigated the reasons for irregular variations in the ball flight path using fluid mechanics (Asai et al., 2006; Hong et al., 2010). However, there are virtually no knuckleball studies on the kicking motions or ball impact characteristics; as a result, the mechanisms of this shot have not been elucidated, possibly because this phenomenon occurs at extremely high speeds. Moreover, there are relatively few football players who can intentionally perform the knuckling shot, and even among them, most have low success rates. In this study, we have used a system of four high-speed video cameras to investigate the swing characteristics of the kicking leg while kicking the knuckling shot. And then, we have tried to elucidate the impact process of the kicking foot at ball impact and the technical mechanisms of the knuckling shot through the comparison with the motion of curve and straight shots.