You can find this exercise on page 59 of the book Synergistic Golf.
Exercise Type: DYNAMIC STRETCH
Exercise Category: ABDOMINALS, BALANCE, FLEXIBILITY, HIPS, LEGS - FEET, LOW BACK
Stand with hands on hips and feet hip distance apart. Inhale to prepare. Exhale and lift right leg out to side maintaining straight posture. Inhale bringing leg back down and exhale lifting other leg to side. Repeat 10x alternating legs.