Bat Kinematics in Baseball: Implications for Ball Exit Velocity and Player Safety

Ball exit velocity (BEV) was measured from 17 experienced baseball hitters using wood and metal bats of similar length and mass but different moments of inertia. This research was conducted in response to safety issues for defensive players related to high BEV from metal baseball bats reported in the literature. Our purpose was to determine whether metal bats, with their lower swing moment of inertia, produce a higher linear bat tip velocity than wooden bats swung by the same players. Analysis using high-speed videography indicated significant differences in the x-component of velocity for both the proximal (metal = 5.4 m s–1; wood = 3.9 m s–1) and distal ends of the bats (metal = 37.2 m s–1; wood = 35.2 m s–1), p < 0.01. The orientation of the bats with respect to the horizontal plane was also significantly more “square” 0.005 s prior to impact (270°) for the metal (264.3°) compared with the wood bat (251.5°), p < 0.01. Mean BEV from metal bats (44.3 m s–1) was higher than the 41 m s–1 velocity which corresponds to the minimum movement time for a pitcher to avoid a ball hit in his direction (Cassidy & Burton, 1989).