At the Match-Up screen, press Square, Triangle, and Circle to change the icons in the first, second, and third boxes. The numbers below indicate the number of times each button is pressed. Press the D-pad in the specific direction to activate the code.
Log bat:0-0-4 Up
Wiffle bat:0-0-4 Right
Mace bat:0-0-4 Left
Rubber ball:2-4-2 Up
Maximum speed:0-0-3 Left
Maximum power:0-3-0 Left
Maximum batting:3-0-0 Left
Big heads:2-0-0 Right
Small heads:2-0-0 Left
Unlimited turbo:4-4-4 Down
Tournament mode:1-1-1 Down
No fatigue:3-4-3 Up
Rocket Park stadium:3-2-1 Up
Coliseum stadium:3-3-3 Up
Pinto Team:2-1-0 Right
Todd McFarlane Team:2-2-2 Right
Eagle Team:2-1-2 Right
Rocket Park Stadium
When you have picked your team and you opponent then on the bottom of your screen you should see 3 symbols. Push triangle 3 times, then X 2 times, then O 1 time. When you have done that then push any directional arrow on the D-pad and it should say Rocket Park Stadium on the bottom of the screen.