Fight as a bear:

At the Main Menu, press Right + Square, Right + Triangle, Right + Circle, Right + X. If you entered the code correctly, you will hear a 'whooshing' sound. Then select any boxer to play as a bear.

Big head mode:

At the Main Menu, press Left + Circle, Left + Triangle, Left + Square, Left + X. If you entered the code correctly, you will hear a 'whooshing' sound. Now all non-licensed boxers will have enlarged craniums.

Regain energy:

When given a choice to hit the heavy or speed bag between fights, hold L1 + L2 + R1 + R2 to regain two to eight points of energy, depending on how long the buttons are held.

Giant boxer:

Create a boxer in Career Mode named PSIRULES. Save the fighter, and then reset your PlayStation. Now load the boxer in Career mode and you'll find his skills and size have increased dramatically.

Cheap Win:

Start any bout in the Career mode. Knock down your opponent and at the same time press Start. Choose to be the loser of the fight. If done correctly, the computer will make your opponent the loser.