How can I properly detect a ball moving in a film capture?
First, for removing shadows try to normilize your RGB image prior to converting it to HSV color model. For more information on this regard see :
http://aishack.in/tutorials/normalized-rgb/

In case the ball is always moving, Optical flow would be a good option I guess. Simply calculate optical flow and mark the region with highest flow as the ball.

The other option would be emplying a tracking algorithm, which, I feel MeanShift would be a good option here. However, a tracking algorithm requires you to pinpoint the object of the interest in first few frames. If the object is fixed (it's always the same ball) then tracking would diffinitly work.