You can find this exercise on page 175 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 tailbone or sit bones. Lift legs off floor with knees bent. While maintaining balance and keeping spine flexed with abdominals held tight, take ball around legs in a figure 8 pattern 10x. Reverse direction 10x.