Football is not a game that is conducive to brotherly feelings for ones opponents. No game is, really; have you ever seen a group of ten-year-olds playing Sorry?
It's very hard to retain perspective on things during a game, to remember that the people across the ball from you are people you almost certainly would love to have on your side. This is a problem with church ball, famously, but it's not just that. Competitive sports are hard to square with the gospel of Christ. I still play, but something in me wonders if the part of me that loves the game would still love it if there weren't someone to beat, if there weren't a loser to make me, therefore, a winner. The idea behind the Gospel is for everyone to win. This would make a football league hard to administer, though.
I know our boys are not out there saying "yea yea, nay nay" instead of swearing. I know that there's a good deal of trash being talked, and worse. I can't say that I admire it, but I understand it and wonder if it might not be unavoidable.