[tongzilla]

I think Homer is referring to the Left Wrist during Impact Interval. In this case, the Left Wrist should always be Vertical/perpendicular to its associated Basic Plane, depending on the Hinge Action used -- Horiztonal, Vertical or Angled.

Palm faces plane for Standard Wrist Action (10-18-A). That's why Swingers need to Swivel -- Uncock then Roll -- to get ready to apply their selected Hinge Action (usually Dual Horizontal) at Impact.