Hamstring is it cramp or a strain or what?

I have a problem with my left hamstring,when i do a quad stretch my hamstring tightens or cramps up.I play cricket and after bowling 4 overs today i felt my hamstring tighten up the pain is not in the belly of the hamstring but just above the knee(it feels tighter and harder than the right leg) i ice up for hours and the next day i feel fine and can do hamstring stretches but doing the quad stretch i can feel my hamstring tighten or cramp.What is wrong with me can anyone help?