If it were between a man and woman who knew each other I can't imagine myself doing anything other than calling the police regardless of the situation. Most likely they do that shit all the time then make up and the cycle of abuse continues. It wouldn't surprise me if she got mad at you for defending her. These bitches have serious issues. NOW, if I saw a stranger attack a lone woman then I would feel the need to get involved, but as far as interjecting myself into a conflict between a couple, forget about it.