Left wrist controls ball flight
By Tim Mahoney

All golfers from a PGA Tour Player, Jason Day, Jordon Speith and Rory McEllroy to a 18 handicap participants in a Troon Golf Academy are striving for control of the golf ball via distance, direction and trajectory. Control is the number 1 ingredient to lower scores and enjoyment.  I have been coaching a two clubface swing for over 30 years: golf club face and the golfers left wrist.  In order for the club face to be square at impact (looking at the desired target) the golfers left wrist needs to be flat (parallel to your lead arm).  This alignment will allow for maximum control of distance direction and trajectory throughout the entire flight.
Left wrist control starts at address with the proper grip.  Left hand heel pad on top, thumb to the right of center and no gap between the thumb and the base of the hand. As you place your right hand on the club: lifeline covers your thumb, trigger finger to the side and no gap between your thumb and the base of your hand. Both V’s in your grip pointing to your right shoulder and both wrist at address slightly bent and relaxed. 
As the club swings, arms swings and wrist cock up the top of the swing the left wrist flattens into a neutral position.  This flat position aligns the club face, positions the left arm into a planned position.  As the club swings into impact the left wrist must maintain the flat position.  This flat position controls trajectory, distance and direction. 
Impact position the left wrist is flat, hips open and shoulders are square.  Shaft is forward leaned and the club face is square.  Control is the effect of a left wrist flat position.