You can find this exercise on page 193 of the book Synergistic Golf.
Exercise Type: DB STRENGTH
Exercise Category: CHEST, POWER PRODUCTION, SHOULDERS, STRENGTH
Stand with feet hip width apart with elbows bent at your sides and 3-5-8lb dumbbells in hand. Punch with your right hand across the left side at same direction as left foot. Shift weight to left foot and lift right heel (pivot). Do not hyperextend or bounce elbow. Pull arm back in and repeat other side. Increase weights when needed. Repeat 20x each side.