My leg will be feeling fine during practices and games when I run, play catch, etc. But when I go through my pitching motion, on flat or mound, and when, or close to, releasing the pitch a sharp pain in the back of my upper leg. It instantly goes away when I return to my regular upright position and doesnt hurt to run or anything like that. In games it isnt a problem for some reason (adrenaline maybe?).
Id like to know whats wrong because I believe I am holding back a little bit in terms of throwing my fastball at 100% effectiveness.