Cheat menu:
Press L, R, L, R at the pre-game menu. This must be done before inputting any cheats below.

Now enter the following codes at the pre-game menu...

Alternate Skies		C-Right, A, Z, C-Up, L, R, Z  
Aluminum Bats 		R, A, Z, B, A, L, L 
Red Bats 		R, Down, B, A, Right 
Blue Bats		B, L, B, A, Right
Crazy Ball 		C-Right, A, Z, B, A, L, L 
Crazy Pitch 		C-Right, A, Z,C-Up, R, B
Devil's Thumb Stadium 	Right, A, C-Up, L, A
Easy Homeruns 		L, A, Down, Right
Easy Steals 		C-Left, A,Down, C-up, Z 
Psycho Bats 		Z, B, R, A
Varied pitches		C-Right, A, Z, C-Up, R, L 
Low gravity		Up, R, A, L 
Increased gravity	Up, Down, L, Up, R 
Fast game		L, A, Z, R, B, A, L, L 
Slow game		Up, L, L, B, A, L, 

Bonus teams:
At the Title Screen, enter C-Right, A, Down, Left.

See Credits:
At the Title Screen, enter R, A, Z, R, C-Right, A, B.

Hidden Messages:
At the Title Screen, enter C-Up, R, B, B.

Thanks to Revolution readers Pyro24x7@aol.com and Michael K.!