content: combination of a tight grip and centrifugal force. As you move in the circular motion, G forces are generated pushing you away from the center of the circle. The faster you move, the greater the g forces. In this particular video, you see him kind of linger at the peak, before falling back down and making a full circle. As his speed decreased at that midway point, he probably felt gravity start to pull him back to earth.. that's where the gripping comes in handy.