Mission: Armada
After the first section of the level, you will end up going through some hallways and end up on the deck of the ship again. This time you will see a bunch of enemies in front of you, on the edge of the ship next to some shipping containers.
To get this achievement, sprint towards them, and find an enemy that is very close to the edge. If there isn't one, just wait until the chopper drops off an enemy, and he will zipline very close to the edge. Once they are close, go up and melee them, sending their body flying off the edge of the ship and gaining the achievement!