Perfect Kill
From Halopedia, the Halo wiki
Perfect Kill is a medal in Halo 5: Guardians multiplayer. It is awarded for killing a full health enemy spartan with without missing a shot. The medal only applies to the Battle Rifle, DMR, Magnum, Halo One Magnum, Halo 2 Battle Rifle, Carbine and LightRifle, with each having its own unique medal variation.