What high-level pitchers do is “let their middle carry them forward”. A drill I have my pitchers do is have them stand on an elevated platform(4-6 inches), and have them shift their weight forward with the muscles in the lower torso, pelvic area(ie: shifting their hips towards the plate). As they begin moving out have them hold their front leg up and fall or “sit” out into footplant while staying balanced(chin over belly button between both feet). Once they get used to this move, you can have them start in a stretch delivery position with feet shoulder width apart. Then, have them pick their front leg up as they would begin the windup and have them use the same action as listed above out into footplant. This drill not only helps with moving forward into footplant, but it also from the platform “forces” the back knee down and in and puts them in a much better position to finish their rotation when the front foot comes down, and as you progress to the 2nd part of the drill, you want to watch the back leg and make sure it is in the same position as when they use the platform. If you push off the rubber, it can and often times will not allow your back side to work properly in finishing the rotation. Similarly if you have a hard push in the stride portion of a swing, it interferes with optimal rotation. Hopefully this wasn’t too long-winded. Hope it helps.