How a lower trail hand opens your shoulders
In the speaker's opinion, golfers commonly end up with their shoulders aimed left. He explains it this way: ball position runs from the middle of the stance to the lead shoulder, and as ball position moves forward the trail arm reaches more and the trail shoulder gets in front. Because the trail hand sits lower on the grip, the trail shoulder moves a little ahead of the lead shoulder - an effect that grows with a more forward ball position.
Channel: PorzakGolf
Watch official source at 8:39