Boxing Match

The World Quest in this achievement requires you talk to the NPC 'Extra Buff Peon" and then collect crates as he follows you.

The Alliance version of this World Quest has them talk to their NPC "Burly Deckhand" to do the same.

Just obtained this myself, and from what I can tell, you must simply kill an Alliance player's NPC without your own NPC dying whilst in War Mode. The NPC has around 123k health.

Quick solution for getting this Achievement during Shadowlands!

I spent 20 minutes trying to get my friend's Alliance toon into the same phase as my Horde toon so I could get the very last BFA world achievement I was missing. We failed. Don't do what I did. Simply bring one of your opposite faction toons to the world quest zone, grab your Peon/Deckhand, and exit the game in the same spot as your other character, quickly log back in to your main, grab your Peon/Deckhand and murder your still logging out toon's NPC. WM on of course!

With Shadowlands being out now the BFA zones are absolutely dead. Hopefully this helps some of you. Good luck!

During the World Quest Crate n' Barrel Alliance Players get a Burly Deckhand and Horde Players an Extra Buff Peon to carry the crates.
Find an Alliance Player and kill his follower to receive the achievement.