You learn this in kindergarten:
"Keep your hands to yourself."
It's really just that simple. Keep your hands off. Doesn't matter who you are, who's involved, gender, sex, class, financial situation, context, location.
Striking how this is such a complicated issue. I understand that statistically, men assault women more often, but in reality, there's problem a ton of men who don't report assault due to not wanting to be labeled a plethora of negative connotations by peers, "bros" and just the imminent society in general. Then, the double-standard often sees such claims thrown out in court or the woman gets a lighter sentence. It's just stupid.
Let's just not hit. So much less complicated if we all respect personal space.
Self-defence, OK. But if no one hits in the first place, self-defence wouldn't be an issue.
Oh, the ideal world.