You can find this exercise on page 281 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: BALANCE, CHEST, POSTURE, SHOULDERS, STRENGTH
Start in plank position. Place feet on top of ball either pointed or flexed. Maintain straight plank body and balance on ball. Perform as many pushups with correct form as possible. Inhale down and exhale up. 10-20 repetitions is the goal.