There has been some inquiry into how to play shuffle (replacing the backpedal) in Cover 3, so here is a quick example of shuffle work with a run-through demo of the back-5 pattern-match drill discussed earlier.
Now, although this player is good at shuffle, he is extending with the downfield foot. Ideally, it should be a push off with the upfield foot (left) and a catch with the downfield foot (right). Because he is extending / reaching with the upfield foot, he will be prone to over extending and consequently clicking the heels (bad leverage position/base). This also makes the transition more efficient and fluid. When the trail foot is the downfield foot, you can use it to direct the body like a rudder (rather than it being the 'drive-train'). Force is initiated by the upfield foot, after the 3 pushes (and come to balance) from the upfield foot, all the defenders needs to do to bail is pivot the downfield foot 45 degrees and this will pivot his hips and put him in a running position downfield. This is not unlike a handoff transition in a relay (baton).
Also, we flew through the 5-DB drill for the sake of filming it (as a visual). We went about 3/4 speed. In practice, this will be full speed and a little more intense.