Unlock boxers:
     Enter these codes as your name in career mode.

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 
100%            Full attributes in career mode 

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.

To Bite your opponents ear off:
     Clinch them by pressing R1 and L1 at the same time and then press
X, Circle, Square and Triangle at the same time. Remember this takes a
point  off  and  if  you  do  any  more  illeagal  moves after you get
disqualified.