What Causes Popping In Shoulder Joint On Excessive Stretching Of Arm?

I am an athlete,and In a football game last year i reached out for a block and heard my shoulder pop and felt a dead arm type syndrome,it weared off and I ignored it.About a year later i was playing basketball when i went up for a rebound with my arm outsretched and bent back i felt another pop with pain,and every time i put excessive force or outstretching it like catching a football it pops and hurts .Please Help