This is THE struggle when instructing. Couple of thoughts in making the transition from static to dynamic movements...
- Create overlapping drill movements. Example: Don't allow your DD to reach the top of her backswing in drill. Start backchaining the motion later than usual... only removing the hand from the side once her forward STEP (not leap) is well established. Her forward momentum should pull the arm "out of the backswing".
- Incorporate a lean prior to stepping forward. Start with both feet on the plate... pitching side foot at a 45... and have her start to lean/fall forward. As in 1... have her keep her hand from moving (backchaining) until the stride foot leaves the ground. It should be a struggle (and a goal) to get to Show-It position.
- Perform "Rocker Walkthroughs". There is no leap... just a forward step. The key... and the MAIN FOCUS of this drill is what I call 'Big Toe Kinematics'. The heel of the 'drive' foot must only make a rocking movement over the big toe.. AND ONLY travel forward. It (the heel) cannot move in any other direction. Simply rock it up. You'll notice that this articulation (when performed correctly) creates knee flexion... which allows the throwing-side leg to be in the throwing lane. Be strict... the heel can only raise up... and ONLY TRAVEL FORWARD. Any other movement is an immediate fail.
- Don't let the front foot rotate the back foot. Stepping into a 90-degree plant makes it difficult for the rear foot to rock up and over the big toe (shoelaces to catcher) as noted in #3. Plant at 45 or less. She might square out a little... but that's ok - as long as she knows that her torso (four corners) must stay still.
#3 is your transition drill... but without proper performance of the others... it's a very, very long road. Slowly add juice to the walk-through. Don't forget to toe-out A HAIR when doing them... but be sure it's not too much... as excessive toe-out makes external rotation of the femur easier... which will pull the throwing-side leg out of the lane... and is easily the one of the largest reasons kids can't find brush (the heel travels rearward, then forward... figure-4 kicking.... crow-hopping... etc.)
I wish I understood this more. I have no doubt it does but I'd love to understand how this plays in to transitioning to BI and IR mechanics.