Mindjack

This is done simply by shooting the player in the head as soon as they hack into an NPC. If you get a perfect headshot on the 1st try then they'll go down. It's easier to do it as Blue to a Red player because they are constantly hacking into other bodies as the bodies they are in get killed. I personally got this achievement without even trying to earn it. I was just playing thru the campaign my 1st time and someone hacked in as Red and I was just trying to put them down as fast as I could so they were less of a threat. I was actually in the process of shooting the NPC they were hacking into while they were hacking into it. So for them is was just a matter of hacking into the wrong body at the wrong time.

Easiest way I found to do this is with a co-op partner on the Red team.

load up 2-1 Panic Room. Red player hacks the first Squawker on the floor level and run upstairs so the other NPC on Blue doesn't kill him. Then Blue follows up to the top of the stairs. Take out the Blue player and wait for him to re-hack the down character and quickly headshot or combo takedown and the achievement is yours. Should take about 2 minutes to unlock.