In sports, the control of friction between an equipment and the body is important for improving performance and preventing injuries. In baseball pitching, friction between fingertips and ball is expected to affect pitching performance such as ball spin rate and ball velocity. In this study, the behavior of a baseball during the ball release process was captured by a high-speed camera. Normal and tangential forces applied between the fingertip and the ball during the ball release process were estimated by dynamic image analysis. Fastball pitching trials were performed with a single subject under different lubrication conditions between the finger and the ball. The ball spin rate was affected by the lubrication condition between the fingertip and the ball whereas the ball speed was not significantly affected by the lubrication condition, which indicates that the friction between finger and ball significantly affects the ball spin rate. Furthermore, the use of rosin powder significantly increased tangential force applied to the ball under wet condition.
