There's an issur de-orayta against injuring a fellow human being, even if he/she permits, and even if it's self inflicted (though mechila does have ramifications for the chiyuvim.
Wonderful, so we're not allowed to play any contact sports, right?
I heard that R' Lichtenstein (who was quite the baller in his day, mi-pi ha-shmu'a) distinguishes between sporting activities where the violence is incidental (baseball, basketball) and where it's an integral part of the game (boxing).
This latter category constitutes real chabalah.
Some might argue that violent contact is incidental in the game of football.
That's crazy naive.
High school kids in Texas are trained to be monsters.
Players dance in celebration after beating opponents like rented mules.
And it's worse than violent movies, because here the violence is real and valued. No "kids can distinguish between reality and fiction" nonsense here.
Implication: I don't think it's a good idea to participate in, encourage, or otherwise promote the culture of college and professional football. Bad chinuch, as they say.
You're better of just watching the halftime show.
Incidentally, it amuses me how these upstanding 'family men' get all bent out of shape about how they want to enjoy a good, clean game of football with their little tykes without having to worry about any 'wardrobe malfunction'.
I'm not just saying this because my team didn't make the playoffs.
I grew up watching football. My kids won't.