In bowling coaching, it is effective to visualize pitching trajectory because the ball trajectory is directly related to the score. In this study, we developed a technique to track the ball in a pitching video and calculate the ball trajectory using the Kalman filter and the background subtraction method. The ball trajectory can be visualized by projective transformation on the pitching video and superimposed on the current trajectory and past trajectories of the ball thrown by the player. This study aims to contribute to the development of applications for the practice of ball pitching.