The amount of forearm rotation in your golf swing is more of a preference than a right and wrong. Players including Raymond Floyd and Nancy Lopez used a lot of forearm rotation in their swings. The swings of modern players including Tiger Woods, Scotty Scheffler and Xander Schauffele possess a more passive forearm rotation. But first let’s describe what forearm rotation is. Stand at address position with your arms hanging down and your palms facing each other. Now as you swing your arms back rotate your forearms 90 degrees in a clockwise direction so that at waist high your thumbs will be pointed upward. Now swing your arms to the left while rotating your forearms 180 degrees in a counter clockwise direction. At waist high in the follow through your thumbs will again be pointing upward. Make continuous swings with your arms only from waist high to waist high allowing the forearms to rotate clockwise in the backswing and counterclockwise in the forward swing. Now grip a middle iron and make the same movements. At waist high in the backswing the toe of the club will be pointing straight up. In the follow through at waist high the toe of the club will again be pointing straight up. When swinging the club back and through notice how your right palm and the clubface remain parallel to each other. This movement demonstrates an active forearm rotation – 90 degrees clockwise in the backswing, and 180 degrees counterclockwise in the forward swing.
In a swing with passive forearm rotation the forearms do not rotate either in the backswing or the follow through swing. Again stand at address position with your arms hanging down and your palms facing each other. As you swing back because there is no forearm rotation as you reach waist high your hands are parallel to your spine, and your thumbs will be pointing at 10:00 o’clock. Now swing your arms to the left with no rotation of your forearms. At waist high in the follow through your hands will again be parallel to your spine, and your thumbs will be pointing at 2:00 o’clock. Now grip a middle irons and make the same movements. At waist high in the backswing the clubface will be parallel to your spine and the toe of the club will be pointing at 10:00 o’clock. In the follow through at waist high the clubface will be parallel to your spine and the toe of the club will be pointing at 2:00 o’clock.
I would recommend experimenting with both type swings to see what works best for you. As I mentioned earlier it isn’t a right and wrong, but rather a preference and there are great players using both methods.