There's not a lot to rest on here... Confrontation happened after daughter left bathroom, he talked to security about it (who apparently couldn't be bothered to get a no-trespass order?), guy was pointed out by daughter, guy was confronted, non-involved witnesses said attack continued after initial punch, fled scene.
Eight years seems generous.
A court proceeding is done in a vacuum. Prior behavior unrelated to the case at hand is customarily forbidden, as it may prejudice the jury.
Not saying it's right, but that's what the legal system has devolved into. A rap sheet ten miles long has no relevance to this case.