Nikon D300 User Manual page 720

Effect of Lens Movement
Lens movement (especially with long lenses) can be
misinterpreted by the camera as subject movement. In that
case, predictive focus tracking is tracking your camera
movement while simultaneously trying to track your subject.
Attempting to handhold a long lens will drive your camera
crazy. Use a vibration reduction (VR) lens or a tripod for best
results. Nikon says that there are special algorithms in
predictive focus tracking that allow it to notice sideways or up
and down movement and shut this process down. So,
predictive focus tracking is not activated by the D300(S) for
sideways or up and down subject movement or panning.
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