From Halopedia, the Halo wiki
Yoink is a multiplayer, campaign and Firefight medal in Halo: Reach that is awarded for killing an enemy while they are in the process of being assassinated. It is the opposite of Showstopper, which is gained by killing an enemy that is in the process of performing an assassination. Though the medal can be earned by interrupting an enemy's assassination in Free-For-All and Multi-Team games, in standard team games the only way to earn the medal is to steal kills from teammates.
- Its appearance is superficially similar to the Maybe Next Time Buddy achievement in Halo 3.
- Its name is a reference to Red vs Blue in which when a character steals something, they say "Yoink!"
- The word Yoink! is used on the Halo Bulletins and Halo Waypoint's forums to censor curse words, similar to Blam!.
- The Yoink medal does not appear in Halo 4. Though players can still kill players who are being assassinated, no special medal is awarded. It is possible the medal was discontinued because 343 Industries did not wish to reward players for stealing kills from teammates.