Weaken the grip toward neutral for better impact
The speaker recommends weakening the grip, moving the thumb closer to down the middle of the shaft and just off the side into a more neutral position. He says this lets him reach a good impact position with the knuckles down and the face square, and that weakening the grip leads to better impact and a squarer club face that isn't pointing at the ground too much.
Channel: SagutoGolf
Watch official source at 5:14