The answer is exerting the minimum amount of force required to end combat. If a woman is beating the shit out of a man, I would not fault him for striking but he MUST stop the moment he is no longer on the defense and GTFO.
Always try to defuse the situation before it gets physical, defend yourself when necessary only AS MUCH as necessary (the best defence is not being where the fists are), never assault anyone. Pretty simple rules to live by no matter who you are.