I would definitely attack, and that would not be a nice situation for anyone involved. I'm not as fit as I should be, but I am ferocious. I don't fight like people in some kind of fistfight; if someone is fighting with me I assume they mean to kill me, and everything I do is intended to do as much permanent harm as possible. I go for eyes, the throat, and the genitals. I bite and scratch and spit. I will try to chew someone's throat/jugular out like a dog. And, I won't stop until the person is physically incapable of getting up again.
Also, firearms. So if I can get to one of those I will use it.