The Cannonball is a best-selling pitching aid. It's one of the most popular and easiest ways for strengthening, toning, warming up of the shoulder and arm muscle. It's also helpful in rehabilitation or therapy for the shoulder and arm muscles. The Cannonball is great to be used as a quick warm up before the game or use it against a wall to develop arm strength or loosen key muscles to prevent injury. It weighs 1 pound and is composed of solid rubber.