Instructions
Join a "Firefight Versus" game lobby from the "Halo: Reach" multiplayer menu.
Equip a shotgun. While a "Bulltrue" can be earned with any weapon, the shotgun is best suited for the task.
Kill an opposing player who is wielding an energy sword when they are mid-lunge. You are guaranteed a kill if you wait to fire until the enemy's body completely fills your weapon reticule.