The windshield wiper is one of the first moves that any up-and-coming contact juggler should learn. It is a foundational move that allows the juggler to learn many more contact juggling tricks, such as the butterfly.
The windshield wiper is simply rolling the ball from the cradle, over the the finger tips, into the palm, and vice versa. The elbow remains almost entirely stationary, and the hand flips over in an arch (much like a windshield wiper, hence the name). The juggler can build up to the fluid flipping motion by at first tossing the ball into the air as the hand flips over, and catching it again as the hand comes down. Then the tosses are made smaller and smaller, eventually disappearing altogether as the juggler learns to roll the ball smoothly over the fingertips. As with any move, it is important to practice this with both hands. This move is often confused with the butterfly; however, in the butterfly, the elbow movement is very flexible and the arch becomes a figure eight pattern, in contrast to the straight arch of the windshield wiper.