I'm going to skip out on a date to watch a football game.
Why would you want to skip the date?
It's an important game and I don't think it's fair for me to give it up just to go on a date.
I think it is rude for you to do that. You should consider the feelings of others before backing out on plans. You could always invite her to watch the game with you and go out afterwards.
I don't want to lose my fandom over this. I'm going to watch the game instead of seeing her.
I really think you should consider inviting her to watch the game, instead of completely backing out of your date. I'm sure she was looking forward to spending time with you, and would be really upset if you didn't want to see her at all.