Drag Back is a trick in PES used to evade your marker by bringing him towards and then turning away from him. There are two variations of the trick.
 Drag Back 1
An easier and simpler version of the drag back where you only have to press DOWN twice from the position you are facing and then forward in any direction.
 Drag Back 2
This is performed by pressing DOWN from the direction you are facing once and then either once to the LEFT or RIGHT depending on the foot of the player really quickly. It can only be performed when you are standing stationary. Only a few players can perform this such as Lionel Messi, Damien Duff and Cristiano Ronaldo.
Here is Damien Duff performing the trick.
 Drag Back 3
This trick is performed by pressing DOWN from the position you are facing and then either LEFT or RIGHT forward DIAGONAL.
It is shown here at 1 minute and 25 seconds.