Nice Work Dawg!

Nice Work Dawg! is an achievement in Halo: The Master Chief Collection. It is unlocked by earning a total of 2,500 Assist medals in multiplayer; this includes both matchmaking and custom games. Spartan Ops missions are considered custom games, as are custom Firefight matches. Assists earned in Firefight matchmaking do not count. The achievement is worth 5 Gamerscore.

Trivia
The achievement's name probably comes from a line frequently spoken by Marine NPCs in Halo: Spartan Assault.