Keep the right knee back to stop flipping
Keeping the right knee back longer through impact lets the trail wrist stay set (the wedge stays 'in the wrist'), which eliminates flipping and lets the shoulders move quicker, so you swing faster with less effort. Presented as one of the best iron tips, applying to irons and driver.
Channel: SagutoGolf
Watch official source at 34:31Why this context matters
Coach demonstrates the move on the range; the narration points to his wrist and knee.