In baseball, the ball repeatedly hits a bat, glove, ground, etc. Such impacts, especially the ones with the bat, affect the ball's velocity and horizontal distance Moreover, the impact with a helmet can be dangerous for human head and hence must be importantly considered Therefore, the characteristic of the ball's impact is very important from the viewpoint of its performance and to ensure safety In this study, a model of the ball was investigated for conducting a numerical analysis of the characteristics of the ball's impact with the bat or helmet Various material properties of the model were determined by an inverse analysis using the data of rebounding velocity obtained by an impact test with a rigid body Furthermore, the effect of each material property of the ball on the coefficient of restitution of the ball or on the maximum acceleration of a human head model was considered for the analysis
