Hi!

I'm hoping someone could help me with a good game system or something that could be tweaked a little in order to have an American football style game. Could anyone offer some recommendations?

Blood Bowl?  (Old Games Workshop game.)

Might need more than 'tweaking' to turn into a true football game though.

It's a fantasy-based, violent football game.

I'm sure you can pick up a pdfof the rules free.