From Halopedia, the Halo wiki
This article is about the Halo 2 and Halo: Reach playlists. For the Halo 3 playlist, see Team Doubles.
Double Team was added on the May 2005 update. Players could enter the playlist alone or with a partner, and the maximum players for a game was four. The playlist was ranked and featured both Slayer and objective-based gametypes.
The March 2011 matchmaking update overhauled the Arena system. One of the consequences was removing Double Team's predecessor, Doubles Arena, from the system. In exchange, Double Team was placed into the competitive playlists. Double Team modified game settings to align more with the smaller player amount. The most notable difference is the low amount of ammo placed for power weapons. For example, the Sniper Rifle has only four shots on pickup. Team Size, party size, and local player count are all capped at two players.