This probably won't be a popular response, but hey...
If a woman gave me a close handed punch (ie, not a slap), and I didn't feel like she had a good enough reason, I would probably physically respond. It would, however, be a radically reserved response, never a closed handed punch, as
serious damage could be done - men are strong and women are fragile. However, neither is it acceptable for women to take advantage of this difference and expect no retaliation. Look where campaigning for equal rights has got you

...
I can see situation in which I might slap a woman in the face, or throw her to the ground, or put her in a submission hold. All things which I know
are not damaging. But establish the fact that such action is not to be tolerated. That being done, the liklihood of staying in that relationship would be small.
I would never, ever, ever, instigate any form of violence.
It is worth mentioning, that as well as relationships where the man is physically abusive to the woman, there are also cases of the opposite scenario - where men are abused, its rather pathetic to see to be honest, but it does happen. It is not acceptable on either side of the fence, but retaliation is retaliation, as long as it shows understanding restraint.