This is notoriously hard to earn legit and in the eyes of many, impossible to earn legit, even ridiculously skilled players would find it a challenge if you take into account all the different factors.
Right, so the achievement requires that you kill the entire enemy team, that means you need to kill every person on the enemy team and you're team mates aren't even allowed to inflict any damage on the opposing team. To make it even more ridiculous, you're not allowed to take any damage while doing this, which means you're not allowed to get shot, you're also not allowed to say, fall down a high ledge and get hurt.
Chances are you're not gonna be able to earn this legit, even if you're prepared to sink hundreds of hours into the game and become insanely good, like I said, given all the factors you need to take into account, it's still gonna be ridiculous.
If you opt to boost the achievement, it can be obtained in a private game, unlike the other achievements which require you have a minimum of 8 players, this one requires you to have 10, you have to be in unbalanced teams, 6 versus 4.
If you're going for the achievement you need to be on the team of 4 and kill the 6 players on the opposition, make sure you don't take any damage whatsoever!
If you're looking for boosting partners, check and see if there are any gaming sessions up and running on here, if not create one, from past experience I can tell you, there are plenty of people out there that want to boost this game.