Very simple, shoot some bullets at the Brute until it becomes enraged and starts running, then kill him with an Energy Sword. The achievement is really easy especially at low difficulty but if you have any question please comment below.
EDIT: It seems that they become enraged mainly when they remain the last survivor of the group. I think the easiest place to achieve this is at the beginning of the mission "Uprising", where after few steps from the start you will find an Energy Sword and various groups of Brutes.
I hope this helps.