Got this one legit because TEAM Headhunter makes it almost trivial. I remember the OG achievement being a pain because it had to be done in 8 player FFA. This time around, just queue in social games for Asset Denial and only have Halo Reach selected. Got it in my first game because 4v4 Headhunter makes it considerably easier. As long as someone on your team hits it, you get the achievement. Stay with your team if you have a lot of skulls or protect the guy on your team who does.