I really love this idea! ?I agree that using the?father's job as motivation pulls me out of the meat?of the story, and agree it would?be better to stay focused on the rivalry/schoolmates. The?motivation of the girlfriend being stolen, makes perfect sense to me that it would cause him to want to defeat the other team.
Just had an idea:? If you want us to root for the QB to win the game and defeat the nerd in the end,?it might be a good idea to first have the nerd win?the girlfriend by doing something nerdy and "underdog-ish", that maybe makes the QB look like a jerk, but?then at the end of the movie, the nerd is?exposed for using his underdog-ness to manipulate her (possibly by setting up a scenario where he looks especially nerdy or like an underdog) and the QB, having truly changed, has a chance to win her back. ?I think this would play better than having the nerd do something genuinely heroic or pretending to be cool, but maybe he's not even as nerdy as he pretends to be.
OR
If you want the nerd to keep the GF, maybe the QB finds his own nerdy girl at the end and falls for her.
Hope some of this can be helpful!