Dead Arm or not


My son is 13 and up until this season pitched and played outfield. This season he earned the short stop position. We just finished the season yesterday but about 3 weeks ago he started pitching weird. Arm slot dropped, velocity and accuracy just went bad. He says his arm doesn’t hurt but he just feels weak. Is this dead arm? His elbow is all good and he hasn’t complained of shoulder pain just discomfort and fatigue.

Thanks in advance guys. I just found this page and seems pretty helpful.