My 11 year old son who plays baseball is complaining of a pinching pain in his upper arm (about 3-4 inches below his shoulder). It is located on the outside of his arm (not the front near bicep or back near tricep). He doesn t pitch much...mostly plays third base. He says it hurts when his arm is elevated and when he moves it quickly (escpecially in a downward motion). What could this be and how should I treat?