From Halopedia, the Halo wiki
Brute Force is an achievement in Halo: Spartan Assault. It is awarded when the player finish the objectives using only the Brute Shot, melee and grenades in Operation D, Mission 1. The achievement is worth 10 Gamerscore on Xbox 360 and Windows systems, and 20 Gamerscore on Xbox One. It is represented by a circle with the jaws of a Jiralhanae inside it.