Serena Williams Photos: Picture Gallery of Strokes

Serena's big knee bend prepares her for the upward leg thrust that will add considerable power to her serve. Reaching up after the released ball helps to make the line of her toss straight and to keep her front shoulder and head up while loading up for the swing.

On this particular serve, Serena is using a Semi-Continental grip, between Continental and Eastern forehand, which is somewhat unusual. The closer to an Eastern forehand grip you get on a serve, the less spin you're likely to produce. Serena probably hit this serve with less spin than usual, but still with a significant amount of topspin and sidespin. Contrary to popular misconception, the world's best servers almost never hit a serve flat.