Detection of front-door and back-door pitches in baseball and the characteristics that make them effective

Abstract

Front-door and back-door pitches (hereinafter referred to as “door-type pitches”) refer to laterally breaking balls that move from outside to inside the strike zone. Door-type pitches often induce called strike or weak contact, but they carry the risk of hard hits. However, there are no clear criteria for detecting door-type pitches and their effectiveness has not been verified. This study aims to clarify the requirements for whether door-type pitches are effective in NPB. First, we used data from MLB to construct a machine-learning model that estimates the amount of pitch movement, allowing us to detect door-type pitches in NPB. Next, we tested the effectiveness of door-type pitches and analyzed the relationship between the pitchers’ and pitches’ characteristics and the test results. The results suggest that some door-type pitches may be effective for pitches inducing weak contact, some front-door pitches may be ineffective for slow pitches, and some door-type pitches may be ineffective for pitches that break in the same direction as the pitcher’s throwing arm. These findings can help players and coaches refine and evaluate decision-making of their pitching strategies.