The aim of this achievement/trophy is to kill six zombies either by sticking a teammate with a bolt from the Pack-a-Punched Crossbow, the Awful Lawton, or to get stuck by said Crossbow and get six kills as a result. Because of the fact that weapon upgrades are costly, and the fact that high-level zombies will not be felled by the Crossbow, this is a difficult achievement/trophy.
First, the player must obtain the Crossbow from the Mystery Box. It is available on all zombies levels except for Moon. Next, the player must Pack-a-Punch the Crossbow. From there, the player is able to earn the achievement.
Ideal locations to get the achievement are wide open areas, such as the stage in Kino der Toten, or in the vicinity of Lunar Lander Д in Ascension. When a significant amount of zombies clump together, it is the best time to fire. After a player is stuck, the best course of action is to run into the zombie horde, attempting to kill as many as possible. Juggernog is advised for this approach. Another possible technique is to have one player throw a Monkey Bomb. Then have another player run into the middle of the group of zombies that gather. Before the Monkey Bomb explodes, have the player in the middle of the group shoot the Crossbow. If done at the right time the crossbow bolt should explode before the Monkey Bomb, giving the achievement/trophy. Another easy way to achieve this trophy on the higher rounds, is by making six to eight crawlers. Have one player shoot the "lamb" then have them run into the middle. Insta-Kill is most helpful at later rounds as well.
When the Awful Lawton is fired, the zombies will be attracted to the shot bolt. Thus, the player can also shoot the crossbow away from the players, that way the zombies will temporarily be away from the players. Next, have one player start heading towards the zombies, and the person with the Crossbow shoot at the player. After the first bolt detonates, zombies will head toward the stuck player, allowing for easy kills, as the player will already be heading towards the horde of zombies.