You can find this exercise on page 275 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: HIPS, LEGS - FEET, POWER PRODUCTION, STRENGTH
Stand with feet together and ball in bent arms in front of chest. Lunge right foot forward dipping left knee towards floor. Outstretch arms forward. Pause in this position slightly then push body back to start position by pushing off front heel not toe. Ball then comes back into chest. Alternate lunging legs 20x focusing on erect back and even amount of weight distributed between both feet.