Photo Study of Amelie Mauresmo's One-Handed Backhand

In order for Mauresmo to generate topspin, her racquet head must rise from below the ball. Here, the downward tilt of the racquet's long axis (the line from butt to tip) helps to drop the head lower. The racquet will become horizontal by the time it contacts the ball. Meeting the ball with a dropped racquet head is generally a bad idea, but it's okay to drop the racquet head on the way up as long as the long axis of the racquet becomes horizontal at contact.

Amelie's weight is solidly on her front foot, and her front leg is completing her upward push as her racquet approaches the ball.