Here is a cheap, I mean really cheap sports party decorating idea. It cost me 77 cents. That's right it cost under $1 to make and you only need one thing.... a roll of masking tape.
I did this on my basement carpet which is carpet tiles, it probably wouldn't work as good if you had really shaggy carpet, but it would work on concrete or probably vinyl. I just took the masking tape and made a large rectangle and then made several dividing lines.
Then I added numbers to the "yard" lines and hash marks.
Finally I added "TOUCHDOWN" and some ball pit balls for the game.
The only game we played was the kids trying to roll their ball and get it to stop right on a certain yard line. But I'm sure there is dozens of game ideas that you could use this for. I was going to do a race game but I had about 12 kids so my field was no where near big enough to do that so it was mostly just a decoration.