5TOOLS,
In my opinion, hip rotation (cause) controls the back foot (effect). If you swing in real slow motion they tend to work together but if you swing at real speed, you can tell that the hips turn/rotate/clear first. In my study, I believe professional hitters (when swinging at fastball strikes) clear or rotate their hips so violently that the ball of their back foot comes up during the hips rotation and back down after the swing is completed.
I also think that hip rotation controls the slotting of the back elbow when swinging at fastball strikes.
What do you see?
THop