Guys. Seriously. There are only a couple of cases where it’s ok for a man to hit a woman:
You are in real physical danger.
Someone else is in real physical danger.
She mouthed off after you chastised her for burning your supper!
Yeah, that’s the damn point. As in “if you fucking touch me you will feel my angry righteous vengeance.”
Anybody who wants to step up and play hitting each other games better be prepared to get hit, quite simply. Regardless of your plumbing, if you take a swing at me, I presume you must believe yourself capable of defeating me. Very shortly, we will find out whether you were correct.
As a mythical “Liberal”, I would take the black man in one hand, and the white woman in the other, and hit **Velocity **with both of them. 
My philosophy on fights addresses this quite well. There are only two questions to ask: Did you start it? Can you finish it?
You didn’t start it, so you’re in the clear there.
Then the issue is how to end it. Hitting back might not be the best way to end the fight if something like walking away is a valid option… but if you need to hit back, you hit back regardless of gender.
Men should only hit back when women have achieved complete and total equality! 
It’s far from a freebie; I paid the price of admission as soon as I got hit. At that point it became abnormal - it became self defense.
And I could ask you to define threat. I just got hit and maybe I’m simplifying the OP but I would take that as a threat if it came from another man, a woman, or anyone in-between. As a lot of people in law enforcement can tell you, anyone can be/is a threat depending on the circumstance and that individual. Part of my response will let me know, very quickly, how much of a threat that person is and what steps I need to take from there. Is this something I am best walking away from or is this something I may need to follow through; possibly all the way to deadly force?
Don’t get me wrong; I call some woman a bitch and she backhands me, she got the freebie. But if some female hits me for no observable reason, she gets the same or possibly less in return.
I grew up believing that men should never hit women, but it’s since one of those things I’ve come to realize is sexist. Violence should always be the last resort, but it should also not be eliminated as an option out of dated values. Personally, I’ve been attacked several times and only deemed it necessary to respond with violence once, in most cases, either there was no intention for a follow up to the conflict, I was able to get out of the situation, or a clear presentation of my intent to defend myself was enough to bring the confrontation to an end.
One of the reasons I find this idea particularly sexist is because I was in a relationship where, near the end, she started getting violent toward the end. Her justification was that she was allow to hit me in anger because she wasn’t going to hurt me and men aren’t allowed to hit women, so I’d never hit her back. Sure, she wasn’t able to hurt me, and I’d never hit her, but it is never the physical part of abuse from a loved one that hurts the most anyway.
And the one time I did use violence to end a confrontation was when we were essentially jumped and my best friend was taken down and getting the crap kicked out of him. There was no talking my way out of it or just leaving it alone, and if I hadn’t intervened, he very well may not have survived; at the very least, his injuries would have been much more severe.
It just plain shouldn’t be a question of the genders of those involved. It’s never okay to initiate violence and it should only be reciprocated if absolutely necessary. We’re not 6 years-old anymore, so “she hit me first” is not enough justification, it should be “I was in fear of my safety”.
If I ever hit someone I feel I should be prepared to be hit back. Doesn’t matter if they are male or female.
That’s why I don’t hit folks!