[ThinkingPlus]

How about this Bosslady . . . So the primary lever assembly moves in a circle regarless of how it is driven huh? what? So that would be the case on the backstroke . . . smell me? So there is a certain amount of inertia of the club moving back. Then the player changes directions . . .

At this point is this where the whole deadweight inertia draggin' lil' bruva of clubhead lag pressure point pressure is loaded?

So then what? You continue to spin the flywheelz (dubz) or do you drive the stump?

Is the swinger manipulating Angular Momentum? While the Hitter is overcoming it by driving in a straight line?

What do the physics types say?

You're killin me. Basically, lag is a consequence of Newton's 1st law: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. As you start the club back (overcoming inertia - bonus points in this discussion and probably a Nobel prize if you can give definitive explanation why mass exhibits inertia ) you impart momentum to the club, i.e., put it in motion. When it is time to start the downswing, this motion must be overcome with a force to get the club moving downplane towards our dimpled friend (the ball, not Bucket's Behind). When that force is applied, one feels lag pressure. As long as that force is continually applied, the lag pressure will remain. Lag pressure maintained through impact will result in a collision that is more inelastic (less lossy) than if one had a clubhead moving with a constant velocity (my assertion, et al.).
Once again, I probably am not providing the answers folks are looking for. Sorry if that is the case.