There are legal limits, which are good. I'd say those limits lie roughly where the violence against the aggressor ended in this case, which is to say, he wasn't killed but probably took more of a beating than he would have preferred.
In principle, the fellow who initiated the violence remains the aggressor even when he is losing. Perhaps another way to restate that is that a man who pursues a strategy of aggression that initiates violence remains the aggressor even if forced into the use of defensive tactics.