From Halopedia, the Halo wiki

HINF Medal Counter-Snipe.png

Counter-Snipe is a multiplayer medal available in Halo Infinite. It is awarded for killing an opponent with a sniper weapon while scoped in, and while your opponent is also scoped in to their own sniper weapon.

The medal image depicts an S7 Sniper Rifle, with a projectile penetrating through its scope.