Hammer the nail: turn the lead pocket into a wall
As a visual for lead-side rotation, the coach imagines a wall running up the left side of his body that his hip bumps against. He feels the left pocket turning inside that wall, as if there is a nail in the wall and he is hammering it as he goes through, so the club gets there later; he feels almost fully rotated before the club hits the ball.
Channel: PorzakGolf
Watch official source at 3:54