Impact of slip distance between fingertips and ball on baseball pitching performance under different friction conditions.

This study aimed to investigate the finger-ball slip distance in baseball pitching under different finger-ball friction conditions and to demonstrate how slippage affects pitching performance. 6 experienced pitchers were instructed to throw 4-seam fastballs at approximately 36.1 m/s (130 km/h) toward a target behind the home base. The finger-ball friction conditions varied and included no application, water application, rosin powder application, and pine resin application. The finger-ball slip distance was estimated from images of the fingertips and ball during the ball release process captured by a high-speed camera (2000 frames/s). The slip distance was significantly affected by the finger-ball friction condition. The distance in the water application condition (21.6 ± 5.3 mm) was 142.3% and 163.8% greater than that in the rosin powder (8.9 ± 3.5 mm, p = 0.022) and pine resin application conditions (8.2 ± 2.2 mm, p = 0.002), respectively. In the ball release process, except for the water application condition, the ball was released by hooking the fingertips on the seam, and the ball slid against the fingers. However, in the water application condition, slip occurred throughout the ball release process. The slip distance was negatively correlated with the ball speed and ball spin rate and positively correlated with the horizontal and vertical ball arrival locations. Our findings will provide new insights into the understanding of how a ball is released in baseball pitching under different friction conditions and will lead to improvements in pitching performance.