Avenger is a multiplayer medal in Halo: Reach and Halo 4 multiplayer. It is awarded when a player kills an opponent moments after that opponent has killed a teammate on the player's team. Because this is a team based medal, it is only attainable in team-based multiplayer games or in Firefight Versus.
Earning this medal in matchmaking unlocks the Kat's helmet avatar award.
A player earning the Avenger medal in a Firefight Versus game.