Cheat
Press x 43 times, no more noless, at the main menu. you cam then fight as one of four sumo wrestlers.
Box as a bear
At the main menu, press Right + Square, Right + Triangle, Right + Circle, Right + X. 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. 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.
Taunt opponent
Press R1 + R2 + X.
MegaBoxer
Go into career mode, create boxer and name him, psirules - don't fight. Exit to main menu then load boxer, he will have 100% everything - a heavyweight "psirules" is, 7 ft 5in and 250 pounds.
Career Mode Instant Wins
While fighting in career mode I found a way to always win no matter what. This isn`t a code but a flawless strategy. You must, however, knock the person down. At almost the same exact time as you knock the person out you press start and throw in the towel. Don`t worry, if you pressed start at the correct time the game will, instead of saying you threw in the towel, it will believe that the computer character threw in the towel. It will continue the count down, but at the end it will say that you won by TKO.
Easy way to gain speed, stamina, and strength
When you go to train your guy, pick the speed bag, or heavy bag and go into the match. Then, throw in the towel so it brings you back to the menu where you can choose the speed bag or the heavy bag.Keep repeating this process till everything is 99!
Regain Energy
When you knock someone down press L1+L2+R1+R2+X at the same time, and keep hitting them.You should regain some of your energy.