*Update: According to my experience and the comments below, this achievement is very glitchy. It has never actually unlocked immediately after meeting the requirements, and unlocks seem to be random.
Champions like Viktor, Ruckus, Cassie, or Tyra all have very fast rates of fire and good damage. So when you see a Drogoz on the enemy team, hovering in the air, shoot him down quick- make sure you get the final shot on him, so that your name appears in the kill feed. This means you got the kill, instead of just helping with the elimination.