What causes a softball pitchers arm to hurt at the shoulders?

Answer 1

The most common answer would be it's overused. Our body also wears out if used too much. it is very important to rest and ice the shoulder after several games in a day. Other causes would be improper mechanics and lack of flexibility. Make sure you're doing the correct movement and have proper warm up before and flexibility exercises after.

Know your body, don't force anything if you feel there's something wrong.