Abstract
The purpose of this study was to investigate the relationship between the flight trajectory of the ball and ball spin in various kinds of baseball pitch. Each subject thrown various kinds of their own pitches for three throws each. The pitched balls were recorded using 4 high-speed video cameras. The flight trajectory, ball spin rate, and direction of spin axis were obtained from the video images, and hypothetical flight trajectory with free fall was calculated from ball initial velocity. Equations were obtained to estimate the displacement of the flight trajectory from that of the free fall ball using "decomposed spin parameter" which consists of the ball spin rate, direction of spin axis, and initial velocity (p<0.001). The findings showed that the displacement of the flight trajectory depended on the ball spin rate and direction of spin axis, thereby accurately predictable from the spin. The characteristics of ball spin can be utilized to develop a strategy to alter the flight trajectory.
