Similar happened to me, though I was older at 17, and my assailant was a year or so younger - I always say that he pounded me because he was clearly the better fighter, and a rough and tumble kind of guy but that it was probably pretty clear at that point that I just didn't care and he never came back at me because at the end of it, it would have been clear to everybody that he was tussling on the floor with a loser and his friends & peers were watching.

For much the same reason you don't argue with an idiot.