You can get this just by throwing yourself off the edge of the map and dying. Every map has spots where you can fall off so you shouldn't struggle finding a place to do so.
One thing to watch out for though... when I had taken damage from an enemy and then fallen off the edge (thus giving them the kill), this didn't unlock for me. I had to throw myself off the edge at 100% health. So if you're trying and not getting it, make sure you're at full health and just dying from the fall as opposed to dying to an enemy player.
Edit: Also of note is achievements can only be earned in PVP matches, which aren't unlocked until level 5. If you're not level 5, you're just playing against bots, so try again once you hit level 5 and start playing against real people.