You need at least one other player for this achievement. Local split screen will also work.
Travel to Arid badlands and there will be a location called Arena. It is a bandit settlement/outpost to the left of Fyrestone.
Enter, make sure you and your friend/split screen player are on different teams and win against them in a 3 round match.
Make sure the other player isn’t too far ahead of you in level or you won’t be able to damage them.