This glitch only works in Warzone online when the enemy is down and at least one of your teammates alive.
First get any enemy down and make sure you have your lancer. Tell your team mate to get his pistol out.
Once you start to chainsaw the downed enemy, your teammate has to melee him twice as you chainsaw (shooting him twice works too).
This will not kill him but as you walk back the downed body will follow you.