I cracked a girls wrist once... Fun story:
She hit on me while she was dating my friend. I told her if she didn't stop, I would tell my friend. She didn't stop; I told my friend. She's walking up to me pretty quickly the next day, and she tries to slap me, i grab her hand and shoulder, push her against the wall. "If you don't stop, you'll regret it." She glanced my nuts with her knee (thank god for boxers, or I would have a higher pitched voice today!) and I grabbed both of her wrists in one hand, and pushed them against her chest, knocking her into the wall. She starts wailing and yelling rape. Unfortunately for her, everyone nearby was watching the whole time. Fun, eh?
I didn't want to hurt her, but I'll defend myself if a woman goes on the offensive. I did feel guilty afterwards, but I don't think I was in the wrong.