Feel trail shoulder to trail ear on the backswing
On the backswing, the speaker's swing thought is to imagine the trail shoulder (the right shoulder for a right-handed player) going into the trail ear. He says this automatically gets the lead shoulder turning down and the shoulders turning in a circle, which produces the plane going back and the top-of-backswing position with the hands behind the trail shoulder.
Channel: SagutoGolf
Watch official source at 2:16