Homer said "Hands", page 41 (6th). I'm being more specific.
See 10-2-G . . . Except with a “True” Swing (6-B-3-0) where Centrifugal Force will produce the “geometric” Flat Left Wrist when there is actually a “visual” Bent Left Wrist. That is, the Clubshaft and the Left Arm are in a straight line per 6-B-3-0 and 2-K regardless of the Left Wrist Position