This is a great basketball dribbling drill for younger players to do that are having trouble keeping their eyes up while dribbling the ball. By tossing the tennis ball back and forth with a partner, you force yourself to keep your eyes up. Also, by adding the element of moving forward or backward it makes it that much more difficult.
This is not just a basketball drill for younger players though, because it can be used as a refresher for good ball handlers, or also a way to improve a players hand eye coordination. A lot of bigger post players struggle with having good hands and catching the ball in the post. The walking partner tennis ball toss drill will help them to improve their hands, and help them develop soft hands.