So how much topspin is needed to classify a shot as a "force follow" shot? On a typical follow shot (at soft to medium speeds) the CB hits the OB and then follows its natural rolling path, depending on shot angle. There may be a tiny boost of topspin that helps it along this path, but usually it isn't obvious and we don't see it occur. The inertia of the CB is just enough to keep it rolling in a natural direction.
If we hit the same shot with a medium-firm stroke, there will be noticeable topspin on the CB after it hits the OB. The CB will have more inertia (more rotational force) and will be forced along a more narrow path in relation to a normal rolling path. This of course depends on the angle of the shot -- on thinner cuts the CB retains most of its momentum, which overpowers the rotational torque/spin on the OB. On thicker shots the CB's rotational force overpowers the amount of momentum that doesn't get transferred to the OB. On a more full hit, it doesn't take much speed to force the CB along a more narrow departure path, because nearly all of the momentum was transferred to the OB on impact and the CB''s inertia is now the driving force that keeps it moving. If we hit the shot harder we get more spin, and it's more noticeable.
Anyway, I guess I'm just curious as to when a shot can be classified as a force follow. I mean, anytime the CB is forced off of it's natural departure path (due to it's rotational spin/force/inertia overpowering it's momentum), we have a forced shot -- the CB follows a forced path instead of a natural rolling path. But are we only to consider it a "force follow" if the topspin is so extreme that it causes the CB to dance against the rail a time or two?