At any time during a game, press the START button to pause and enter any of the following codes at pause menu:

Code - Effect

Right,Down,Up,Left,Right,Left,Down,Up - Big Head
Right,Right,Down,Up,Down,Up,Down,Left - Fast Running
Down,Left,Down,Up,Right,Left,Right,Down - Max. Speed Pitches
Left,Right,Up,Right,Up,Left,Right,Down - Slow Running
Left,Right,Down,Up,Right,Left,Down,Left - Small Heads