Pitching form evaluation based on elbow position by a monocular camera

Pitching in the correct form is essential for preventing injury and improving skills. It is not easy for athletes and instructors to check whether a pitcher is throwing in the correct form. In this study, we record a pitcher from the direction of the catcher by a monocular camera and estimate the skeleton pose of the pitcher by using OpenPose. We propose a new method to evaluate whether the pitcher can pitch in the correct form by examining the estimated pose. We use SSE(Shoulder, Shoulder, Elbow)-line as an evaluation index. When the upper body of the pitcher faces a batter, the SSE-line should be straight. To find the right frame at which the pitcher body turns squarely to the batter, the distance of the shoulders in a video frame is used. When it becomes the largest, the shape of SSE-line should be measured. Since the motion of the pitcher was fast, we use a 240 fps camera to investigate the relationship between the shape of SSE-line and the shoulder distance. The relationship between the shape of the SSE-line and the shoulder distance with the 240 fps camera was evaluated, and we discussed their pitching properties based on the evaluation.