Designed to help a junior or beginner -grown transition, Green Starter Ball has a lower compression for slightly slower, more playable bouncing properties. This ball bounces 25 % lower than regular tennis balls, giving players a greater opportunity to refine their blows and focus on the form as they continue to develop their game. This is a fantastic ball to use with 25-inch to 27-inch tennis rackets. The jar contains 4 balls.