Best way I found was you need to have your Assault team close enough to the enemy so that they can throw hand grenades at the enemy. I would suggest go to level 3 "Five-Oh-Sink" to get this achievement. Move your assault team close enough without firing a shot. When you get close enough and you command the assault team (Left Trigger), you should see a red hand grenade when you move it over an enemy. Repeat this 4 other times and the achievement pops.