Cheats:
At the Match-Up screen, press , , and 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
More time after play   1-2-3 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
Horse Team             2-1-1 Right
Todd McFarlane Team    2-2-2 Right  
Eagle Team             2-1-2 Right 
Lion Team              2-2-0 Right 
Terry Fitzgerald Team  3-3-3 Right

Thanks to Revolution readers Scott, Austin Parker, Nate Dogg, Buggz, Josh, and Marcus!