So, unless they really are anti-gay/trans, the only reason to have this kind of ruling might be to keep the male players that they want to keep out from cross dressing and getting in anyways. That's the only situation that I can think of (aside from them possibly actually being ignorant dicks) that would prompt a ruling like that.
Now, here's the thing: This is not a game or whatever that men are inherently better at than women. They probably want to do this type of event for the same reason that gay bars exist; sometimes people want their own version of something where they can do what everyone else is doing but with people of similar interests. Women (of all types, even those with male anatomy who identify as female) just want to play a game they enjoy with fellow females. If a man cross dressed (posing as a trans woman) just to get in so he could stomp on women in a game, he's pretty much doing the same thing as faking mental retardation to win the special Olympics (sorry for sounding like I'm saying women are like mentally retarded people, just hear me out.). The social stigma of pulling a stunt like that pretty much assures that it won't happen. It would put a big old sign on his neck saying that he thinks that women suck at League, and that he needs to validate himself by beating them. Sometimes you really don't need real rules to keep people out; social mores keep a lot of people from doing bad things naturally.
