At the Main menu, hold R and press Right[x3], Left, Right
Like the title said, the following codes are only for the NTSC version of the game, its might not work in other versions.
All Arenas, All Movies, and 28 Boxers : Right, Right, Right, Left, Right, L
Double Speed Boxing :Hold R and press Down, Left, Down, Up Right, and L.
Punches Do Double Damage : Hold R and press Right, Down, Left, Up, Left, and L
Unlock All Boxers and Arenas : Hold R and press UP, DOWN, DOWN, LEFT, LEFT, L
Maximum Stats (Tournament and Exhibition) : Hold R and press LEFT, UP, UP, DOWN, RIGHT, L
Maximum Stats (Movie): Hold R and press RIGHT, DOWN, DOWN, UP, LEFT, L
ENTER ALL THE CODES ONLY AT THE "MAIN MENU" OF THE GAME.
Double Punching Damage- Hold R-shoulder and press (on the D-pad) right, down, left, up, left and l-shoulder.
Double Speed- Hold R-shoulder and press (on D-pad) down, left, down, up, right, and l-shoulder.
Unlock all boxers- Hold R-shoulder, and press (d-pad) Up, down, down, left, left, l-shoulder
Superhuman Movie Mode- Hold R-shoulder and press )(d-pad)right, down, down, down, left, l-shoulder.
At the Main menu, Hold R and press Left, Up, Up, Down, Right, L
Enter the following code at the main menu: HOLD R and then press up, down, down, left, left L