Rise of the Kasai

There are a few places where this can be unlocked but the best place that I found was in level 6, Vaitaku, within The Keep (the third) sub-area. Within this area are 2 locations where there are 3+ enemies statically placed underneath hanging barrels. In other words, they do not roam until you alert them.

The very first switch that Griz will pull (if the computer A.I is in charge of him) is to the South East of your starting location. This small switch location is perfect because there are 5+ enemies standing directly underneath hanging barrels. Use a range weapon on the lever that holds the barrels. Do this without alerting them and you will easily unlock this trophy immediately.