The following codes must be entered in the Cheats option from the Options menu. Enter Options, and press R or L until Cheats appears. Press down until you see the cheat you want and press B to get a keypad.
All Freestyle tracks
All National tracks
All Supercross tracks
Turn on the "Bowling mini-game" cheat. Go to Smoke Ridge in freestyle. Find the purple "S" and head north. You'll see a football game.