Skunked!

Skunked! (Skunked in Halo: The Master Chief Collection) is a Multiplayer achievement in Halo: Reach and Halo: The Master Chief Collection. This achievement is awarded when a player wins a game of Invasion in the first phase. It also unlocks the Invasion Nameplate in Halo: The Master Chief Collection.

Following the shutdown of Xbox 360 Halo online services on January 13, 2022, this achievement is no longer attainable in Halo: Reach.

Walkthrough
Winning a game in the first phase is only possible while defending in a standard Invasion match, not Invasion Slayer. To unlock the achievements players must successfully defend the two marked territories in phase one on Boneyard, Breakpoint, Spire, or Forge World.

Trivia

 * The only way to earn this is to play as the defending team in Invasion (for instance, the Spartans on Boneyard) and stop the attacking team before they complete the first phase objective.
 * The title of the achievement refers to a sports rule where one team has an insurmountable lead over the other team.
 * The announcer says this if the Spartans prevent the Elites from completing the first phase on Breakpoint.