that's because the gene for liking sports is on the y chromosome.
Any girl who likes sport either

a) actually likes sportsmen in little shorts, or
b) is actually a man
( Master Of Turnips. Only gays and morons believe in ghosts., Wed 8 Jul 2009, 20:50, archived)

I've known a few who:
c) pretends to like sport so boys will like her.
( The Cat's Mother Not a People Person., Wed 8 Jul 2009, 20:55, archived)