So here is another straightforward solution brought to you by DCM7734:
Have a 2nd controller, or do this with a friend. It doesn't matter.
Mode: Warzone ( 10 rounds, if with a 2nd controller, 20 if with a friend, that way you both can get it )
How to get the achievement:
Go straight, When you get the the bridge where you have to turn, there will be some frags there. Pick them up. Now, run to the other player, ( just keep following the path... they should be at the other end of the map ) and pistol whip them 3 times. They should go down. ( Do not mash the button, or it won't work... you'll kill them. ) after they are down, and crawling, pull out your frag grenades that you picked up on the bridge. press B to tag them with a grenade, and quickly press A to pick them up. It'll say you've won the won... about 2 seconds later, your opponent will blow up, and you will get 1 of 10 progression points for this achievement.
Rinse and repeat 10 times, and POP!!! Achievement.