Monster Home Runs
With this trick you'll get a homerun with every hit! During a game or in the Home Run Derby, press and hold R1 + R2 + L1 + L2. While still holding those buttons, quickly press Up, Up, Triangle, Triangle, Up, Up, X, X. You will hear a chime if you did the trick correctly. This trick is hard to do and may take repeated attempts.
Mystery Stadium
Go to the stadium select screen and press L1, R1, L1, then hold R1 and press Start.
Super Batter
For a super batter, create a custom player named "Erik Kiss" and trade him to any team you wish. Erik can hit the ball out of the stadium with ease.
Super Center Fielder
Create a new player named "Dennis Hirsch" and put him at center feild. He run 4 times faster than a regular player!
Super Pitcher
For a super pitcher, create a custom player named "Jon Spencer". Trade him from the free agents to any team you want. Jon can throw up to 159 mph pitches!
Super Players
For super ball players, enter any of the names from the credit screen.