[Max Impact]

I don't get it either. The upper left arm (not the wrist) rolls naturally from the ball and socket joint at the left shoulder as it swings on an inclined plane, thus producing clubface roll on the plane. Rotating the torso, with no independent left arm swing, to swing the club on the plane, produces the same clubface roll effect. I'm not even sure that it is anatomically possible to manipulate the left shoulder joint to prevent that roll in a swing of any force, while keeping the shaft on the plane. But why would you want to anyway?