Just because the Club has hit the ground does not mean that it has reached its lowest point. That lowest point does not occur until the Clubhead is in front of the Left Shoulder (and further Down Plane, i.e., further down in the ground).
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I found it easier to understand hitting down and the low point once using the reference of the clubhead passing the left shoulder.
Prior to this point if I understand it correctly you can in fact be driving down cause the force originates from the body (hands, arms, shoulders). The reference to the ground is artificial, especially if the horizontal reference is not parallel to the power generating force.
I believe this concept is the rationale behind setting up on slopes such that the shoulder follow the slope.
If one agrees that the low point is when the clubhead passes the left shoulder, then one can understand how the clubhead can actually be moving upward yet it still be a motion that is hitting down, maybe not on the ball, but it is a hitting down motion force from the power generator.
I believe that this often adds to the confusion on golfers who haven't reach the low point with the driver but swear they are hitting up.
Low point defined as ??? When the primary lever has reached full extension - Placing the clubhead furthest from the left shoulder ???