Via A Voice For Men
Why this double standard? We hope you won't call us misogynists when we say that Mother Nature is a bit of a bitch when it comes to women. Humans in general tend to be pretty equal in lower-body strength, but when it comes to the upper body, men are on average about twice as strong as women. And since most hitting is done with the upper body rather than with a series of acrobatic kicks, this gives men an advantage that just isn't sportsmanlike. It's similar to why it's socially unacceptable to punch children in the face. Most children are smaller and weaker than most adults, so whereas in movies like Home Alone and Dennis the Menace a child hurting an adult is played for humor, the opposite usually doesn't fly.
Above: A child who you should probably not punch in the face.
But there are women who are stronger than men, you say! Yes, and there are also children who are bigger than adults, but societal norms tend to be based on generalities. For example, everyone can agree that it's frowned upon to yell at complete strangers on the street, but it would probably be OK if you were warning a stranger that there was a bear behind him.