Could i explain it like this: Basal ganglia basically initiates the correct/appropriate movement But cerebellum doesnt trust the basal ganglia thus corrects that initial movements pathway. For the cup example: basal ganglia says alright gonna move the arm and then grab the cup, for that i have to send this much stimulus. cerebellum still modulates it on the fly using your proprioceptives and sees if indeed your hand is actually reaching the cup or not.
As wanted movent is brought by by B.G and sequence of movemnt is planned by cerebellum then Whats is role of Proprioceptors through spinocerebellar pathways in taking up cup....