A fastly moving baseball, viewed from the side on a baseball telecast, shows equally-spaced faint artifacts, tangent to the trajectory, before and after the central image. Why?
I think it is due to motion processing attempting to remove the blurring of moving objects. It processes a window of frames and tries to produce an image that has the object without the motion blur that would have been present. This can result in artifacts which some people find objectionable and might be the cause of the artifacts you have observed.
Aha, so the frame rate of my TV sufficiently undersamples the motion of the ball that a blur would appear. Clearly, a zero phase noncausal filter used because there is a pre-echo, and it’s symmetric. But I’d still like to know something about the details of that filter.