It is thrown off by the right shoulder moving down the selected plane, correct?
I would say it is (the left arm),thrown off the chest by the pivot.
Please remember my first post in this thread, -I stressed that my comments are from a swingers perspective.
I am well aware that this is the Hitters domain ,but I responded because I detected a confusion of components-maybe wrongly.
However ,from a swinger -it is all PULL-therefore "chain reaction"