I was a goalkeeper and stopped a read fast ball with my hand. my hand fold all the way back and since then my hand hurts when i fold it to the back. every other movement is ok. what can it be?

Sprain/strain: How long ago was injury? It sounds like you strained/strained your wrist (well, more correctly, a ligament/tendon/muscle). Cold packs are useful immediately after an injury. Since all other movements are ok, I'm less suspicious for fractures & dislocations. But if pain persists or gets worse or prevents you from doing your normal daily activities, I'd recommend seeing your Family Doc or Sports Med