Grand slam batter
Create a player and enter "SLUGGER" as a name. He will always hit a grand slam if batting with the bases loaded.

110 mph pitches
Create a player and enter "STRONG ARM" as a name.

Homerun sounds
While running around the bases after hitting a homerun, press Triangle to hear a soft horn, Square to hear a loud horn, or Circle to hear a whistle.

All-Star teams
At the team selection screen, hold L1 + L2 + R1 + R2 and press Up, Triangle, Right, Circle to unlock all-star teams from 1970s, 1980s, and 1990s. If you entered the code correctly, you will hear a sound.