No normally on a drag route the route drags in front of the QB and over the middle. But if you put a running back on a drag route it originally is over the middle, but here's the trick. When you motion the running back from one side to the other after you audible the drag, it sets up a quick flat route behind the line. It is the only way I know to set up this route and the only coverage I know against it is man cover. I have also seen a DE contain knock this pass down, but I don't think many people DE contain on nano.
Actually I should have said audible the drag route then motion RB to other side (in my previous post). My mistake. Its fixxed now.