Cheats:
At the Match-Up screen, press B, X, and Y 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.

More time to enter  3-0-3 Up
Rubber ball         2-4-2 Up 
Soft ball           2-4-2 Down 
Ice bat             0-0-3 Up
Sword bat           0-0-2 Up
Bone bat            0-0-1 Up
Log bat             0-0-4 Up
Wiffle bat          0-0-4 Right
Mace bat            0-0-4 Right
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 
No contact mode     4-3-3 Left
Sub-Zero            1-2-2 Down
Rodeo Clown         1-2-3 Down
Little League       1-0-1 Down

Thanks to Revolution readers Big Sal and Marky Marky!