>>> jack, could shoulder rotation initiate the swing then tht? <<<
For batters that initiate their swing from the normal launch position, shoulder rotation and tht are initiated at the same time. However, some batters have the bat vertical or cocked forward toward the pitcher. They apply mechanics that accelerate the bat rearward before they initiate shoulder rotation - I refer to this mechanic as PLT (Pre-Launch Torque). Below is a post from the Archives on this topic.
PLT to THT