You will need to complete the quest "The Raid" in the Desolation of Mordor DLC in order to get this achievement.
"The Raid" is broken down into two parts. In the first part, you will need to collect all of the coin from the wagons and kill all of the marked Orc guards, and you can get a bonus for killing five Orcs by using Were-Wyrms (you can get them to attack nearby Orcs by shooting the Were-Wyrm mounds, which are blue bumps on the ground that you can see while aiming).
In the second part of "The Raid" you will need to break 15 grog barrels with your sword or shield to spill the grog on the ground (shooting them will make them explode, which doesn't count) in order to attract "the Rumbler" and complete the mission. You will want to stay in motion to avoid the attacking Were-Wyrms as you go - each time you break a grog barrel, a Were-wyrm will attack. Once you break 15 grog barrels, you'll get the final cut scene and the achievement will pop.