starts and stops and collisions with the ground/bases/etc that cause the injuries. Overhand Pitchers are in high demand and the body is not designed to throw that way that many times. Its all body mechanics and the stress on the shoulder and elbow - even with great pitching mechanics the stress is there every time. Rule nowadays is that time off when small injuries happen is better than pitching through them because small turns to larger later for many...then its surgery which is 50-50 on a comeback. Go out and play catch with someone at 90 ft for 30 minutes and tell us how the arm feels the next day...you might get it better...lol!