When talking about rotation, as it pertains to the golf swing, you must bring up the hips. The hips, as well as the rest of the lower body, play an integral role in becoming a consistent ball striker.
When many of my students are posed with the question: "What starts the downswing?" They usually reply with "the arms", or sometimes "the shoulders". Very rarely do they answer the question correctly...The correct answer? The lower body. More specifically, the hips.
The first move on the downswing starts with a slight "bump" of the hips, in which the left knee and hip bone make a slight (very slight) move to toward the target (See Fig. 1). After that slight move toward the target happens, the next move is a sort of twisting (AKA rotation, See Fig. 2) move in which your belt buckle rotates (there's that word again!) toward your target in order to make room for your hands, arms, and shoulders to be released down and through towards your target line.
Staying in line with my rotation philosophy, its important to mention, that although the hips are, in fact, slightly moving towards the target, you should be hitting against an imaginary wall that goes from your left foot, upwards, perpendicular to the ground. In Fig. 3, you will see the complete movement of the hips on the downswing.
If you can master the correct hip motions on the downswing, you will most certainly find that you will gain more distance and be a much more consistent striker of the ball.
Hopefully this helps further explain the role of the hips as it applies to ball striking and a strong rotational golf swing.
Until next time,