The achievement unlocks when you kill your 50th bandit. There are different bandit groups in each region. In the Dalentarth region where you start the game, the Red Legion controls the area. Doing the Recipe for Trouble
side quest given by Nanne Hanri
, owner of the Golden Alchemy Age shop in Gorhart, and the Commendation
faction quest given by Ost Ordura
(found on the first floor of the Gorhart Inn) will pit you against enough bandits to get the achievement. These quests are available at the beginning of the game as soon as you enter Gorhart. Below, is a very short video showing the achievement unlock on the 50th bandit kill.