I've seen some hitting instructors say that the player is driving their back knee towards their front leg/ankle ect. I'm not sure anymore? Initially the hitter might make this movement. But I believe once the front foot is planted, the force of the back hip rotating causes the back foot to come forward by pulling it. Thoughts?
Reason why I ask this is because I believe in my DD's swing she is overemphasizing this push and not focusing on rotating her hips/core enough. This causes her hips to slide when they should be rotating ... power leakage IMO.