You can find this exercise on page 47 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: FLEXIBILITY, HIPS, LOW BACK
Stand with feel wider than hips. Hold big ball over head while maintaining good posture (shoulders down, ribs lifted, belly button pulled in). Bend knees to squat position while bringing ball down to touch floor, then stand and bring ball back up overhead. Resembles a woodchop motion. Inhale up and exhale down. Repeat 10 times.