Start a match anywhere with 2 controllers. Perks off, hammers on as only weapon.
Beat both players down to minimum health.
Then both take a hammer. And have the players stand at max throwing range, facing eachother (you can test this out first by throwing a hammer and picking it up again.
Throw the hammer with the controller of the player that are not going to get the achievement, and then throw the hammer of your maincontroller right before getting hit.