The first thing you need to do to set-up the backdoor cut is make a couple of jumpers. Preferably long ones, drawing defense way out from the hoop. Now you’ve given the defense a reason to want to stop you from catching the ball. You’re killin’ ‘em from out there! Next, you walk the defense down toward the block or wherever. The defense is thinking, “oh, he’s walking me down to the block because he wants to pop out, catch and shoot. I know what he’s doing”. When you’ve got space to do so, you pop out, i.e. make a quick move away from the hoop. The key now is to recognize, almost f-e-e-l when the defense’s momentum has them slightly out of control. A defender who is running out to stop you is easy picking. A defender who is low and in “the stance” is a little more difficult to breakdown. Sometimes you can go backdoor after going out just one step, sometimes more. The key for you is to change direction as the momentum of the defender is moving away from the hoop. As she is pushing off to take a next step or slide out, that is the moment when you want to ‘quick’ change direction and go to the hoop. Also, and this is subtle but important, your outside foot, the one that is planted and pushes you toward the hoop, should pivot slightly as it lands so that the toe points in the direction in which you will run. (That’s the case with every change of direction or v-cut.) Additionally, it helps to start the process of putting your hands up as if you are putting them up to catch a pass. Remember, it’s change of speed and change of direction. Slow, slow, slow, like you’re doing nothing, like you’re Mickey The Dunce, and then, bang, quick to the hoop, timed to go against the defender’s momentum.