http://doylestown.patch.com/groups/sports/p/doylestown-girl-s-petition-to-play-football-gaining-steam Can you imagine what will happen if the boys tackle her. They would probably enjoy it if they're not gay. I don't see how it's permissible to allow girls to be subjected to such boys. Especially many of them are probably black males who are stronger and tougher than whites in general and especially white women.
Besides the modesty issue, it seems like the boys could hurt her physically. If girls want to play, they should play in a girls league. Football isn't like other contact sports because it requires contact as an integral part of the game.