The amount of stress imposed on shoulder and elbow appears to be directly correlated with the degree of maximum shoulder external rotation (MER) during throwing motions. Therefore, identifying risk factors contributing to the increase of MER angle may help to decrease the throwing injuries occurrence in baseball players. The purpose of the present study was to demonstrate the correlation between MER and the kinematic variables at stride foot contact (SFC) during the early cocking phase, the passive range of motion (ROM), and the shoulder strength. The subjects were 40 high school baseball players. Each subject carried out five throwing tasks with his maximum effort. A three-dimensional analysis was performed to obtain the MER, and the shoulder angles of external rotation (ER), extension and abduction at SFC in the early cocking phase. The ROM and muscle strength of the shoulder ER and internal rotation (IR) were also measured. Significant moderate linear correlations were found between the MER and the ER (r = -0.32, p = 0.04) at SFC, extension angle ( r= 0.35, p = 0.03) at SFC, IR strength (r = -0.30, p = 0.04) and passive ROM of ER (r = 0.46, p = 0.01). The shoulder IR and extension angles at SFC may determine the degree of the MER angle. Furthermore, weak IR muscle strength and excessive ROM of ER might be risk factors for shoulder and elbow injuries. The finding will enable us to establish better prevention and rehabilitation strategies for throwing injuries in baseball players.