Domestic violence; Is it ever ok for a man to hit a woman?

Society as a whole and a lot of our own mothers have probably ingrained in we men's brains, it's never okay to hit a woman. Obviously if a woman initiates an attack or other sort of crime on a man there's a level of self defense said man can utilize.

I'm asking you to remain anonymous and only offer real life scenarios you know of b/c you witnessed it, or your best friend who you trust told you about it. But hide behind the real people involved if it was really you. If you've not been in a similar situation pretend you have been. Tell me when or if it's okay for a man to hit his significant other.

The ultimate question here is the following scenario: A man has become angry with his wife and struck her in the face. She is unconscious and lying on the ground. Is there a difference between:

She burned dinner because she was talking on the phone too long and not paying attention and she was struck with a closed fist. The man knew she was talking to a family member on the phone, not another possible lover.

-OR-

She's been lying, coming home late without valid explanation, frivolously spending the man's money, and screaming over dirty clothes and dishes since they've been living together. She screams in his face over the last bit of dirty jeans on the bathroom floor and gets open handed slapped across the face.

Obviously you can tweak and modify those scenarios a lot of different ways. You can take her PMS or other stresses into consideration. But are there times it's ok for a man to strike his s.o.?