You can find this exercise on page 104 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: ABDOMINALS, ARMS - HANDS, STRENGTH
Walk out over top ball to a balanced plank pushup position. The farther you walk out toward your toes, the more challenging the move. Once balance has been achieved, pike hips directly in air hinging from the hips. Keep legs as straight as possible. Return to plank and repeat 10x. Maintain posture of upperbody. Walk back to kneeling over ball after the 10 reps.