When is it okay for a man to hit a woman?

I now hate this imaginary woman.

Well, you might be able to prove a motive if there are no eyewitnesses. If the woman hits hard enough, it might leave a mark. Evidence or no evidence, hitting people is illegal. Not just women.

A woman's slap will leave no mark on the man. If he uppercuts her in the jaw, that WILL leave a very visible mark. Most girls slapping guys are making an emotional statement. Comparing a woman's slap to a guy's uppercut in terms of bodily injury is ludicrous.