Coefficient of restitution for normal and oblique impacts

Engineering of Sport 15 - Proceedings from the 15th International Conference on the Engineering of Sport (ISEA 2024)

The coefficient of restitution (COR) is an important metric for describing the liveliness of softballs. Only softballs that meet COR regulations set forth by governing softball associations are allowed in play. This is done for fairness as well as safety for the players. Softballs are tested in accordance with ASTM F1887-14. This standard states that a softball is projected normally onto a flat rigid wall at 60 mph and the rebound speed is measured with light gates. COR is found from the ratio of the outbound speed to the inbound speed. However, softball is a game in which players actively try to put spin on the ball; whether it’s a pitcher adding spin to their pitches with different grips or releases to try and outsmart the batter, or batters aiming to hit the ball in a way that optimizes backspin allowing the ball to travel farther. Therefore, in game situations, a ball will rarely impact a surface straight on with no spin, instead it is likely to bounce obliquely. There has been limited research on oblique impacts of softballs, as most of the focus has been limited to the normal direction. This research aims to study high speed oblique impacts of softballs.