Rock and Coil Hit Back
From Halopedia, the Halo wiki
Rock and Coil Hit Back is an achievement in Halo: The Master Chief Collection. It is unlocked by earning 100 Environmentalist medals in Halo 2: Anniversary multiplayer matchmaking. Environmentalist medals are awarded for kills with fusion coils and the stalactites on Lockdown. The achievement is worth 10 Gamerscore.