Classification of four pitching styles in Japanese baseball players

This study aimed to provide normative biomechanical data of baseball delivery styles and to verify an appropriate criterion for quantitatively classifying baseball pitches into four delivery styles. In total, 74 pitches were visually identified by seven coaches into 24 overhand (OS), 17 three-quarter (TS), 21 sidearm (SS) and 12 underhand (US) deliveries. The accuracies of the classifications of the pitches using the arm slot angle (theta(AS)) and using the combination of trunk lateral tilt (theta(T)) and upper arm elevation (theta(A)) angles at release were compared. Average values for theta(AS) were 53.9 degrees, 31.5 degrees, 5.8 degrees, and -34.8 degrees in the OS, TS, SS and US; corresponding values for theta(T) were 31.9 degrees, 15.4 degrees, -0.9 degrees, and -40.1 degrees; and for theta(A) were 39.8 degrees, 16.1 degrees, -6.3 degrees, and-43.0 degrees. Both variables (theta(AS) and the average of theta'(T) and theta'(A), which corresponded to the projection of each point on the regression line) correctly classified the delivery styles, but the accuracy of the classification using theta(AS) (96%) was higher than that using the average of theta'(T) and theta'(A) (89%). There were fewer and smaller overlaps of the ranges of pitches classified using theta(AS) (only 6 pitches between TS and SS (14.9 degrees to 23.0 degrees), which can be considered a buffer zone) compared to the average of theta'(T) and theta'(A). Consequently, theta(AS) seems the most appropriate for classifying baseball pitches into the four delivery styles. The separation points between the four styles were marked by theta(AS) values of 45 degrees (between OS and TS), 19 degrees (between TS and SS) and -13 degrees (between SS and US).