I teach pitching based on Ernie's video's.
I never have seen him teach dragging of the pivot foot. Usually your trying to explode with the left foot if your right footed and snap the hips to end with the right foot ahead of the left one. It would seem like dragging the pivot toe would make the pitcher slow down her hip snap and lose speed.

One on my pitchers is taking private lessons where their teaching dragging the pivot toe.

Does the pitcher have to drag the pivot toe?
Is it illegal for the pitcher to not drag the pivot toe?

Thank You
Coach Howard