Are we comparing a schoolyard fight, where regardless of the outcome you're still just children and will end up in detention, or are we comparing an actual fight.
Because if I am in an actual fight, like against someone I do not know, who has the intention of hurting me for whatever reason, then I have no qualms about kicking him in the groin to prevent him.
It doesn't mean I'm going to mutilate his nether-regions or anything nasty. I'm just going to take advantage of his physical weakness and prevent myself from being hurt. I don't owe this person anything and he's started a fight with me, so why should I show him honour and respect?