[Mike O]

Left arm and left wristcock....

If the left wrist is to uncock on the square plane line in the manner of a sequenced release for a swinger... then the left wrist must remain absolutely turned to the plane prior to uncocking even if that means that the left wrist is bent.:

IF the left wrist is the only thing moving and everything else is not moving- then the shaft would move on the same plane as the left wrist was moving (uncocking or cocking). That's not the case in the golf swing. The left wrist motion creates one vector of many vectors (lots of joint motions) - so the left wrist can uncock on a plane that is different that the resultant "on plane" motion of the clubshaft. For Homer Kelley's analysis of this issue see 2-N-1 in his book- "The Golfing Machine". It seems to me that given the post above and the video link - that there is a belief or implied statement that the left wrist has to be on the clubshaft plane during a sequenced release for the clubshaft to stay "on plane". A sequenced release involves the release of accumulators #2 and #3- there's a lot more going on in the swing besides just those two accumulators- while Accumulator #2 is releasing before #3- there are a lot of force vectors than combine with accumulator #2 to maintain an on plane clubshaft.