Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Jab Master (20 points): Take it up top and land 1000 Jabs in any game mode.
Hook Hero (20 points): Take it up top and land 1000 Hooks in any game mode.
Uppercut Machine (20 points): Take it up top and land 1000 Uppercuts in any game mode.
Stick and Move (5 points): Show me you can dance around the ring kid and move more than your opponent.
Lightning KO (20 points): KO an opponent in the first 60 seconds of round 1 in any game mode.
Twinkle Toes (20 points): Rack up a ring mile.
Swinger (35 points): Keep on throwing punches until your hands bleed! I wanna see 50,000 thrown shots, kid!
Hot Shots (50 points): Achieve 50 Signature Punch KO's in single or multiplayer.
Can't Touch This! (10 points): KD an opponent without taking a single shot.
World Champion (50 points): Become the World Champ in Career Mode.
Ring a Ding Bling (30 points): Earn your first career million.
First Steps (5 points): Turn Pro in Career Mode.
Don King Promoted (30 points): Join Don's Team during your career.
Easy Pickings (20 points): Defeat Nino Basilio.
Judge Dreadful! (20 points): KO Dave Saddler.
One Armed Bandit (20 points): KO Sven Zurilo.
Blind Fury (20 points): KO Vassily Kablov.
3ml of G? (20 points): KO Milton Forrest.
Party Animal (20 points): KO Nyack Quartey after a big night out.
New Kid On The Block (5 points): Create a Career Boxer.
Going the Distance (150 points): Complete Career Mode.
Platinum Puncher (100 points): Complete Career Mode on Champion difficulty.
Xbox LIVE Journeyman (5 points): Win 5 ranked fights.
Xbox LIVE Contender (10 points): Win 15 ranked fights.
Xbox LIVE Champ (20 points): Win 35 ranked fights.
Xbox LIVE Legend (40 points): Win 50 ranked fights.
Long Way Down (42 points): Beat every fighter in Career Mode.
Tournament Champ (30 points): Win a Ranked Tournament.
Who's Winning Then? (10 points): Play ten back to back multiplayer games.

Additionally, there are ten secret achievements:

Signature Smash Down! (5 points): KO another boxer with a Signature Punch.
Training Game Superstar! (30 points): Reach World Champion in all training games.
Loser! (3 points): Lose 3 fights in a row.
Team Calzaghe (30 points): Win online fights as both Enzo and Joe.
Top Form! (25 points): Reach World Champion in any training game.
Switcher (10 points): Have a Southpaw and an Orthodox fighter both get knocked down in the same match.
PERFECT KO! (10 points): Knock out an opponent without taking any damage.
Sinister (5 points): Defeat an opponent using a Southpaw boxer.
Comeback King (10 points): Knock out an opponent who had nearly put your boxer down.
The King of Queensbury (25 points): Complete all Classic Fights.