Greg was a world-class diver until he hit his head on the diving board during one of his dives. He now has difficulty coordinating the movements required for various tucks and rotations. It is likely that when he hit his head on the diving board, Greg damaged his .

Cerebellum

Explanation:

The Cerebellum is the part of the brain most directly linked with the control of movement and coordination. It is a primitive part of the human brain that we share with all vertebrates.

Greg probably damaged his cerebellum when he hit his head because he has problems performing those specific tasks.