Easiest way to get this trophy is waiting till you are on the map Lijiang Tower. Two of the three variations have great spots goat attempt this.
In the Gardens, go to the enemies bridge that they can cross over and hide behind the wall that is near it (it's the wall that surrounds the capture point on either side. Simply wait till you hear the enemy get close or pop out to check every once in awhile, then use your Sound Wave ability to push them off the edge. Immediately wall ride on the wall you were hiding behind and the kill will count towards your trophy. Repeat twice more. If you are lucky you can push people off on the opposite end of the capture point, but focus on the bridge mostly.
There is also the Night Market variation. Here you can camp out in the back of the capture point where there are two entry ways on each side. Many of the enemy players will come down the set of stairs that edge around the capture point to get in through said entrances. Simply peep out or listen for enemies and use your Sound Wave to push them off. Then immediately wall run on the outside wall (I found the inside to be a bit tricky to get the kill to count) and rinse and repeat. NOTE: shoot out the railing along the edges so the enemies will fall off more easily.