Gamma Quick Kids 60 Tennis Ball - 12 Pack The GAMMA Quick Kids 60 Tennis Balls are made for younger players and beginners transitioning from playing half court tennis but still not ready for a full size court. These lightweight tennis balls are 50% slower than standard tennis balls, making it easier for players to get in position and be ready to react to shots for more control and accuracy. They're also a great tennis aid for more advanced players wanting to learn or practice spin on a smaller court or against a backboard. USTA/ITF Stage 2 specification.