During a match, hold L1 + R1 and press Triangle + Circle + X + Square.
Career Mode
Fight yourself or Advance fights.
After you hit X to select your next opponent, quickly tap Up or Down to switch opponents. Tapping Down causes you to fight yourself.
Unlock Boxers
Enter these codes as your name in career mode:
100% - Full attributes in career mode
DOUBLEDAMAGE - Do Double Damage
INVINCIBLE - Infinite Health
KNUCKS - Ashy Knucks
SANDERS - Barry Sanders
GIAMBI - Jason Giambi
SEAU - Junior Seau
NOLAN - Owen Nolan
FRANC - Steve Francis
CLOWN - The Clown
EYE - The Cyclops
GORE - The Gorilla
BULLDOG - The Bulldog
BABY - The Baby