You can find this exercise on page 76 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: ABDOMINALS, BALANCE, CLUB CONTROL - ACCURACY, LOW BACK, RHYTHM - TIMING
Sit on floor holding ball in front of chest to prepare. Round back putting weight just back of tail bone or sit bones. Lift legs off floor with knees bent. While maintaining balance and keeping spine flexed with abdominals held tight, take ball clockwise around both legs 10x. Reverse direction 10x.