Tojo, in my opinion the pitcher should lean into the pitch off of the rubber and generate her push. For a right handed pitcher. as her left (lead) foot lands she should be driving toward the plate, transferring her weight to this left foot. While this is going on the torso and above will be going forward towards the front leg. Just about simultaneously with the release of the ball and slightly afterwards, the force of the torso moving forward (which would be deaccelerating) would allow the right (push) leg to drag forward whereby the left hip flexor would then rotate towards home plate. Then the right leg will slowly come to a stop. The hip flexor finish is something that I require because it gives added torque to the ball. The great ones engage this part of the motion far better than the not so good ones.