The role of cerebellum in athletics?

The cerebellum is involved in coordination and fine-tuned movement. It has many inhibitory neurons which help to make small adjustments to motor control signals sent down the spine, controlling movement.

In the case of athletes, these small movements can mean big differences in direction, strength, etc. in how one makes a Golf putt, swings a bat, throws a ball, etc..

Without these fine adjustments, all of our gestures and actions would be gross movements (flailing of arms and legs, and the overaction seen in infants whom haven't yet developed fine motor control yet).