Here is the full list of all 10 Kinect Sports Gems: Boxing Fight achievements worth 50 gamerscore.
Reach level 1 (or observe another player doing so) to gain the rank of Canvas Kisser.
Reach level 2 (or observe another player doing so) to gain the rank of Rope Hugger.
Reach level 3 (or observe another player doing so) to gain the rank of Lightweight Fighter.
Reach level 4 (or observe another player doing so) to gain the rank of Bare Knuckle Brawler.
Reach level 5 (or observe another player doing so) to gain the rank of Power Punch Pugilist.
Reach level 6 (or observe another player doing so) to gain the rank of Heavyweight Hitter.
Reach level 7 (or observe another player doing so) to gain the rank of Contender.
Reach level 8 (or observe another player doing so) to gain the rank of Ring Leader.
Reach level 9 (or observe another player doing so) to gain the rank of Prize Fighter.
Reach level 10 (or observe another player doing so) to gain the rank of King of the Ring.