As far as I know, there is no explicit term in the bible that states that g@mbling, in itself, is a sin. Any issues that revolve around the subject of g@mbling are more closely related to becoming bonded to money specifically. So, given that, I don't think putting $5 in a football pot is going to damage your image in the eyes of God.
I agree with Colleen. Does the fantasy football league support the torture of bunnies or something?? Or is your girlfriend mad at you for wasting your money? lol.
There simply has to be more to this question...why would it be wrong?
I mean is it unchristian or against the bible?