From Halopedia, the Halo wiki
Game Breaker is an achievement in Halo: The Master Chief Collection. It is awarded to players who achieve 10 kills while using the Jet Pack armor ability in match made games.
The name of the achievement is likely a reference to complaints from some players that the addition of armor abilities in Halo: Reach, and the jetpack in particular, "broke the game".
The original concept art used in the achievement art.
