[O.B.Left]

I found the action of his left foot of particular interest. In relation to the camera it is 45° open at address, lifts off the ground and closes to 0° at the top of the back-swing, then opens to 90° on the down-swing.

Sadlowski does the 45 to 0 to almost 90 thing too as I recall. Its the move to 0 degrees that is interesting.......not sure what it signifies.

One guess is "internal left hip rotation". I had a lesson once where an instructor in an effort to get more hip turn out of me, had me lift my left foot off the ground and turn it clockwise two or three times before going ahead and actually swinging. It that same set of muscles which when the foot is grounded cranks the left hip around apparently. Forgot about that one , Im going out to the back yard, swing think tank to try it again right now.