An increasing number of researchers have begun to use depth sensors in their studies due to the drop in sensor prices in recent years. In computer vision, depth provides a wider range of useful information. In sports, baseball and softball pitchers are typically unable to self-evaluate their throw quality when practicing in the bullpen, and umpires are mostly unavailable to evaluate their throw quality. In this context, the present study proposed a 3D strike zone system based on the Kinect v2. The system was able to determine ball speed and throw quality. Recordings were then exported into a visual ball trajectory image including a 3D K-Zone, which can service as a reference for pitchers.