To unlock this achievement you must play the Droid Run game type and capture three droids in one match. Droid run is basically a territory capture game type with a slight twist. The droids/territories are mobile and constantly moving about. You will need to capture the droid by running up to it and pressing and holding the X button on you controller until it has been claimed. There are multiple droids on the map, so it should be fairly easy to capture a total of three droids in one match.