Yes, and it can even happen by accident. When my younger brother was a teenager, some of his friends got into a play fight that turned much more serious than it was supposed to. Two of the guys really went out at it, and one of them ended up in a permanent vegetative state after a hard punch to the face.

The kid who threw the the punch went to jail for a very long time, even though he was beyond remorseful. He was devastated, really.

My brother (and all his friends) were shaken and traumatized. Nobody thought throwing a few punches could have such horrible consequences.