Thug

Thugs are a common enemy that is encountered in the galaxy. They are often hired guns and often don't have armor, but have shield generators and are typically armed with Assault Rifles, Shotguns, or Pistols.

During the mission to expose Saren, Shepard encounters some thugs trying to intimidate Dr. Chloe Michel from telling Garrus about the quarian that had recently visited the clinic. However Shepard enters as they are "talking", and one of the thugs takes Dr. Michel hostage. Garrus then kills the thug and Shepard and the squad assist in taking out the remaining thugs.

Thugs are again encountered during the assault on Chora's Den. Fist had apparently hired some thugs to defend him from Shepard, but they are all killed in the attempt to defend the bar against Shepard's assault.

Tactics
Because thugs possess little shielding or health, taking them down is relatively easy. However because you usually encounter them in groups, they can overwhelm you so make sure to keep an eye on them. They are also the type of enemy that stay in cover more than the rest of the enemies that you will typically encounter, so you have to make sure that you either eliminate their cover, or force them out somehow.