[Jeff]

The question is why does the left wrist appear cupped (bent) when one first turns the left hand on the grip so that the palm faces more groundwards at address, and then cocks the wrist upwards.

I believe that is is due to an anatomical re-arrangement of the wrist alignment due to forearm rotation (pronation). If one holds the flat left hand with fingers outstretched so that the back of the left hand is vertical, then any upcocking and downcocking wrist movement is a "pure" cocking movement (radial and ulnar deviation of the wrist at the radio-carpal joint). However, if one first pronates the left hand (which is a forearm movement and not a wrist movement) before gripping the club and then grips a club (producing a turned hand grip), and then performs the same vertical-to-the-ground cocking movement of the clubshaft, then the left wrist will bend (dorsiflex) because the cocking movement is occurring across the plane of the wrist joint, which is turned to the right secondary to a forearm rotary movement. To perform a "pure" cocking movement that will not produce bending of the left wrist in that turned hand situation, then the club must be cocked in the plane of the wrist joint - so if the left hand is pronated 30 degrees (which rotates the wrist plane 30 degrees), then the club must be cocked in a plane that is 30 degrees to the right.

Jeff.