For this achievement you need to be the last surviving hunter in "Quickplay" mode.
Therefore, you need to eliminate atleast the last hunter which is with you on the map. It does not matter if you were the first to activate the wellspring for this. You can aswell kill the wellspring-carrier and then survive until the end of the round by either killing everyone else or waiting for the time to run out.
This can be done quite easily by being the first to activate the wellspring, so hurry up with those rifts. Then, get yourself some good guns and defend your position.
Otherwise, I recommend to wait for everyone else to kill each other to eliminate as many threats as possible. Then, use your shadow vision to see the last remaining hunter and eliminate him.
The achievement should pop right away.