Keep the right arm glued to your side, no chicken-wing gap
The coach points to how the right bicep stays connected - 'glued' - to the side through the backswing, so that as the right forearm folds no space opens up at the top. He warns that 'chicken wingers' who let a big gap open between the armpit and the right arm will never be consistent and will spend time making up for that motion.
Channel: SagutoGolf
Watch official source at 0:49