Swing your club to the top of your backswing. If your right arm (right-handed player) forms a perfect right angle, chances are your left arm is in a relatively extended condition. This is an example of a good backswing radius. Radius, in fact, is a speed source. Try again, only this time purposely cause your right arm to completely collapse. Notice now that your left arm also now sags. the radius of you back swing is almost non-existent. the right arm should structure the left in the backswing.