I now plan to demonstrate that the terms "open-closed" mean different things when we are discussing impact versus P4 positions.
Consider a golfer who adopts a neutral left hand grip.
Here is Ernie Els's swing action.
The red splined path represents his traced CH arc.
In his late downswing (or at impact) the left arm and clubshaft are in a near-straight line relationship and the back of the FLW is moving in the general direction of the CH arc (followng the completion of a PA#3 release action), and in the direction of the target at impact. If the clubface is square to the back of Els' left forearm, and his functionally-flat left wrist (= GFLW), at address, then it must also be square at impact - if the back of his left forearm/GFLW faces the target at impact. If his clubface is open at near-P7, or P7, then it means that it is open to the CH arc and ball-target line - and vica versa for a closed clubface.
What would cause the clubface to be open or closed at P7?
One possibility for an open clubface at P7 would be the combination of a GFLW and an under-rotated left forearm (incomplete release of PA#3) at impact. Likewise, a closed clubface at impact could be due to the combination of a GFLW and an over-rotated left forearm at impact.
However, an open/closed clubface could also be due to a bowed/bent left wrist scenario.
Imagine a golfer (who uses a neutral left hand grip) having a square clubface at impact - left-hand diagram. The black dot represents the left shoulder socket. The green line represents a straight left arm that is vertical at impact. The red line represents his clubshaft that is straight-in-line with his left arm at impact. The grey line represents a functionally-flat left wrist, which faces the target at impact if the back of the left forearm faces the target at impact (which should happen if the PA#3 release action is completed and the left forearm is not under-rotated or over-rotated at impact). Under those conditions, the clubface (violet line) must also be facing the target at impact and it must be square to the ball and CH arc if the ball is placed at low point (nadir of the clubhead arc).
Now imagine that the golfer unintentionally acquires a bowed left wrist during his downswing action that causes the clubface to be 1" behind the ball when the left arm becomes vertical and when the PA#3 release action is successfully completed - central diagram. Note that the clubface will be open relative to the ball-target line, and ball, at P7. It not due to any change in the degree of gamma rotation that happens naturally during a PA#3 release action, and it is simply due to the bowed left wrist deformity.
The right-hand diagram shows what happens if the golfer unintentionally acquires a bent left wrist deformity during his downswing action - his clubface will be closed relative to the ball-target line at impact.
Note that the degree of open (or closed) clubface
in the horizontal plane due to this acquired non-FLW scenario depends on the accumulator #3 angle - being greater for a more horizontal VSP scenario at impact (compared to a more vertical VSP scenario at impact). By contrast, the consequent degree of change in clubface loft at impact due to left wrist bowing/bending will be inversely proportional to the VSP - being greater if the VSP is steeper.
Now consider what we mean by a closed or open clubface at P4.
Note that at P4, the back of the FLW has rotated so that its not square to the CH arc (moving in the direction of the CH arc) but it is roughly 90 angled relative to the CH arc. Note that the clubshaft is angled 90 relative to the left arm. If the golfer has a GFLW, then the clubface will be angled at about 45 degrees relative to the ground (if the left arm is angled across the shoulder turn angle), but it will be parallel to the circumference of the CH arc. An open clubface is a clubface that is rotated more vertically while a closed clubface is rotated more horizontally - but note that its rotation when open/closed (curved black arrow) is perpendicular to the CH arc (while it was in the same general direction of the CH arc at P7). That means that the terms open/closed clubface at P4 is very different to what we mean by an open/closed clubface at P7.
Now, consider what would cause a closed clubface at P7. One possibility is a palmar flexed (bowed) left wrist - as seen in Dustin Johnson's swing.
Image 1 shows that Dustin Johnson has a bowed left wrist, and closed clubface, at P4. What would happen if DJ maintained the same degree of bowed left wrist throughout his downswing action between P4 and P7? Would his clubface be square/open/closed at P7 - presuming the same degree of PA#3 release action that gets the back of his left forearm to the same angle it has at address? The answer is that his clubface would be
open to the ball-target line at P7 and he has to use a
greater degree of left forearm counterclockwise rotation during his late downswing to get a square clubface at impact.
Note that DJ has a bowed left wrist impact - image 1. Note that his forearm is rotated marginally more counterclockwise - compared to his address situation (see next image).
Note that his left forearm is rotated marginally more clockwise at address (image 1) than it is at P7 when he has a bowed left wrist. This "fact" is counter-intuitive, and many golfers would think that having a bowed left wrist at P4 (which closed the clubface at the P4 position) would mean that he would need
less clubface-closing action due to a left forearm counterclockwise rotary motion in his late downswing (due to a PA#3 release action), but the opposite fact is more likely true - he may need marginally more counterclockwise rotation of his left forearm to get a square clubface at impact.
Jeff.