Shoulder pain when throwing a ball is not so surprising when you consider the complexity of the shoulder joint and what it takes to perform that motion.
To move your shoulder joint, the muscles, tendons, ligaments, and bones all have to move in a synchronized and stable pattern. Because of this, subtle abnormalities can lead to shoulder pain and discomfort when you are throwing or afterward.
This article reviews the mechanics of the throwing motion and reasons it may cause shoulder pain. It also discusses symptoms of a shoulder problem, what's involved in diagnosis, and how it can be treated.