A lot of tough guys in this thread.
Men on average are considerably faster and stronger, carrying a higher proportion of muscle to fat. We have thicker, firmer skin. Our skeletal frame is larger. Our bones are bigger and heavier. We have a higher pain threshold and tolerance level. Thousands of years of contending with violence and aggression from other males has caused us to develop thicker, stronger, foreheads and jaws, much better equipped to withstand a beating. The same punch that might stagger or knockout another man, has a decent chance of killing or seriously injuring a woman.
Yes, you're well with your rights to defend yourself if a woman attacks you, but let's not act like it's the same thing as fighting off another dude.