Far Cry New Dawn - Good Job, Cap Trophy Guide / Achievement Guide - Kill 5 enemies by throwing a shield at them.

Certain enemies, called Brawlers, carry big bulletproof shields. You need to kill them, grab their shield, and throw it at enemies with R3 for a kill.

The best place for this is at the Outpost "The Island" (Rank 3). It's the northern-most Outpost. It has to be at Rank 3! There will be 3 enemies with shields in this Outpost. One is at the north-east corner of the Outpost and two on the boat that patrols the area. Kill these guys and grab their shield. Be sure to have a decent pistol equipped to first damage the enemies before throwing the shield. The shield will cause roughly 50% damage. It's best that you camp behind a corner and let the enemies come to you one by one. Unequip the shield when you don't need it, by simply selecting a two-hand firearm from the weapon wheel. Otherwise, if enemies shoot the shield it gets destroyed. When an enemy is below 50% health you pick up the shield and throw it with R3.

It's worth noting that this cannot be farmed via checkpoint restart or dying! Whenever you die or restart the checkpoint it will reset your kill count. You can, however, capture the Outpost and reset it again to make the enemies respawn. This way it can be farmed. You can easily get 5 shield kills in one run though, because you have 3 shield enemies (thus 3 shields) and they can be used for multiple throws each.