[nuke99]

I choose 2 . Because i feel that the trailing leg/knees is a thrust board, at the end of the backswing the thrustboard "readied" the momentum for your pivot to thrust(slide forward) in the start up. The spine angle should not shift much or at all in the backswing. even though your hip turn excessively, your spine angle should not differ much.

However in the downswing. an axis tilt is required to move the shoulder down plane. Thus its the only time that the spine shift occur.

However It is possible for the spine to be moved in the backswing or through swing. Like for example if the trailing knee straightens during the backswing. if that the case you will have a hint of reverse pivot.