It's not a man vs. woman thing. If you as a human choose to enter a combat situation, you have given up the right to be safe from physical altercation. Done. Just because you wear glasses, or are a little pudgy fellow, or a girl, does not give you the right to initiate assault, but even more, it doesn't exclude you from retaliation.
If you don't want to get hit back, don't hit in the first place, there should be NO exception in this.
That said, I would still think hard before ever hitting a woman back. That choice would not come easy for me. The choice should be there to defend or retaliate. But ultimately, whether a man or woman is hitting you, the noble choice would be always to walk away, if possible.