John, Clint Hill did not jump off the follow-up car till after the head shot. The shot he heard running to the limo sounded different he said and matches the other witnesses bang bang testimony. it also matches the two largest blur episodes on the Z film.
Clint Hill was running toward the limo before the headshot. Because the limo was moving forward, there wasn't much closing speed, but he was already in motion.
Although he was told differently, the only shot he heard while running was the headshot. He said the shot had a metallic sound which indicates to me one of the sounds he heard was a fragment striking the windshield frame.
To the best of my recollection, he was telling his story at the Sixth Floor Museum but I will have to find that program to verify it.