This achievement is to get a very high and quick chain of skillkills to make enemies drop the green intel, the kind you see in multiplayer. There are three levels of intel: blue, yellow, and green. The red intel is actually ammo drops.
Each color is a higher skillkill level of intel. For example, any single kills and up to about x3 will be blue, then you see yellow, then later you see green.
The best and easiest place for this is near the end of the game in the final Target base. It is called the Datacore room. Simply build up a skillkill combo before entering the room by headshotting the snipers or by using whatever means to kill them. Then, plant mines in each of the four corners of the room where the enemies drop out from. This will spawn-kill all four corners of enemies, netting you an instant high combo such as a x14 combo, then run around and search for the green intel, pick it up, and you’ve got it.