Injury to the end of the upper arm bone (the humerus) in young pitchers is called Little Leaguer's shoulder. It occurs most often in the athlete who is still growing. Overuse from repeated throwing causes a fracture in the growth plate.

This injury is related to the frequency and intensity of pitching. Rapid growth of the shoulder growth plate from age 13 to 16 creates a weak area. This puts the young pitcher at risk for injury. Throwing curve balls, a high number of pitches per game and per season are other risk factors.