A ball valve will be forced open/closed by the force of the liquid flowing through it.  (i.e. when the valve is nearly closed the force of the flow will "snap" it closed, and similar for opening.)
I have seen throttled ball valves rattle open (not closed).  It is not a snapping action, but more of an incremental thing.  It has usually taken a couple of hours in strongly vibrating service for a ball valve to go from 5% open to 15% open (where the throttling stops) and then it will tend to stay there forever.  This is one of the many reasons that I will not spec a ball valve for throttled service.
I have done the free-body diagram on the forces on a ball and while it is a bit indeterminate (positive feedback is hard to get into equilibrium), the forces to slam a ball in either direction don't seem to be available in a flow stream, even at high flow potential and very high dP.

MORE NEWS