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.
Unknown
While playing a game, hold L1 + L2 + R1 + R2 and press Up, Triangle, Right, Circle. If you entered the code correctly, you will hear a sound.
Allstars
Go to the team selection screen. Hold R1 + R2 + L2 + l1 and press Up, Triangle, Right and Circle to unlock the teams of the allstars from 1970s, 1980s and 1990s. When you have done this action correct, you will hear a sound.