SPARQ Eye React Ball The Nike SPARQ eyeReact Ball is designed to improve your hand-eye coordination, reaction time, depth perception and first-step acceleration. This ball reacts unpredictably when bounced, forcing you to visually track the ball and react to it's trajectory, much like tracking the ball during a game. Four nodes create unpredictable and dynamic actions. Made of durable rubber, its green color allows for greater visibility when tracking. 2.8" in diameter.