Photo Study of Andy Roddick's Serve

As Andy's elbow has almost finished straightening, the wrist is just beginning to move the racquet toward the straight alignment with the forearm it will have at the point of contact with the ball. The racquet is approaching the ball edge-first at this point, but due to pronation of the forearm, the string bed will turn to face much more forward by the time it arrives at the ball. With the loose wrist and forearm one should always have on a serve, pronation will happen quite naturally as a result of the large forces exerted by the legs, torso, and upper arm.