That's a bit of an extreme case scenerio. Plus, even if there's no rule against hitting a woman, there is a law against hitting anyone. I don't think that a guy who would hit a woman hard enough to kill her would be stopped by an etiquette rule if he isn't stopped by a law.

I suppose there might technically be a guy out there who's strong enough to accidently kill a woman because he doesn't realize his strength, but lets face it, that's not the average joe. And women who have that kind of strength exist too, but there isn't a huge social rule to protect men from those women.

Personally, I think it seems like one of those things that force guys to act tougher than they should have to. No one should just have to sit there while someone is beating them up rather than defending themselves.