Understanding Golf Swing Dynamics

Golf swing dynamics are both active; in the development of club head speed; and reactive; in the control of centrifugal force effects and stability of swing rotation.

Misdirected and/or uncontrolled dynamic effects will cause involuntary distortion in the biomechanics of a golf swing despite a player’s attempt to perform in accordance with their perception of a workable swing concept 

Club head speed at impact depends upon controlled continuing acceleration along a uniform line of action from the top of the backswing. 

Controlled acceleration derives from power generated directly into stabilised body rotation from ground traction through the feet and legs. 

Continuing acceleration along a uniform line of action (on an inclined swing plane) is achieved by up/down arms swing coordinated with body rotation around a vertical axis while retaining wrist cocking.

 Body rotation is stabilised against the effects of centrifugal force and forces deriving from power generation by body weight shift along with retention of appropriate posture (body angles, centre of gravity, etc.).

The retention of cocked wrists in the downswing is referred to  as "lag" in golfing parlance . 

Another important aspect of golf swing dynamics occurs at impactwhen kinetic energy of the club head is transferred to the ball, more or less instantaneously, resulting in a sudden loss of club head speed while the arms and hands continue to move forward  

This causes the leading wrist to involuntarily flatten or even bow out towards the target, momentarily. That occurrence has been observed in high speed photo snapshots.

Based on a misconception that elite players consciously produce that circumstance, as an essential component of effective swing technique; striving for a flat leading wrist at impact is given undue and misleading emphasis in general swing instruction. 

For discussion re other relevantly important aspects of Golf Swing technique go to:-
A logical Golf Swing Concept
Weight Shift in the Golf Swing
Golf Swing Rotation
Flat Left Wrist at Impact
Flat Left Wrist in the Downswing
Or:-
Go from Understanding Golf Swing dynamics to A New Insight into the Golf Swing