You can find this exercise on page 50 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: CHEST, POWER PRODUCTION, SHOULDERS, STRENGTH
On hands and knees, place heavy ball under one hand. Body should be in one line from knees, through hips to shoulders. Perform pushup with one ball on hand while maintain straight line of body. Hold abdominal wall in tightly. Keep chest in alignment with hands. For more challenge, lift knees to straight leg plank position and perform pushups. Switch hands, 10 times.