Well, here's how I would go about: (I would act the same, if it was a guy that just came out of nowhere to punch me)
Public scenario, aka lots of witnesses:
Have myself drop to the floor theatrically, hold my head and whine out in anguish, so everyone sees that I am miserable, so they will testify against him/her later in court.
Once the police arrives, testify against him/her, go all weak-kneed, etc.
Sue him/her for everything he/she got.
Profit.
(I am a 200cm, 100kg guy and a martial-artist specially trained in self-defense, so making the case against a petite woman would be hard, buut if my acting is good enough, I can claim that she got a lucky punch in, and that there should not be a reason for her not to be punished)
In a non-public scenario:
A random human being of a given gender walks up to me, in an environment without witnesses and attacks me (description see above)?
He/she is looking for trouble, which means, that he/she is either very confident in his/her abilites or just plain crazy, which in turn tells me that, whatever the case, I will be in serious trouble if I do not defend myself.
So, I have to hit fast, hit hard and try to surprise him/her.
I would probably start talking to her/him, along the lines of "ouch, why, you §$%&" and before finishing my sentence kick him/her in the shin as hard as possible, hoping for him/her not to be an active Thai-boxer, etc.
If he/she is still standing and willing to fight afterwards, go all out on regions you know will hurt, but, in most cases won't result in anything fatal, so joints, arms, legs, lower stomach.
I do make too many plans for situations like these, thank you for asking.