Go into options when you start a game, then enter: C, C, C, B, A, A, A, B. When you're finished, exit. You'll be at the main screen. Press A and you will then have the option of turning on and off invisible walls.
Passwords
Go to the options screen and enter:
Curve Ball: B, A, C, B, C, C
Super Power: B, A, B, B, B, B, B, B, B, B
Super Goalie: A, A, A, A, A, B, B, B, B, B
Super Offense: A, A, A, A, A, B, C
Super Defense: B, B, B, B, B, C, B
Shootout: A, B, A, C, A, B
Stupid Team: A, B, C, A, B, C
Dream Team: A, A, B, B, C, C, A, A