The Pro Penn Marathon Extra Duty | 24 cans | 72 balls delivers the consistent bounce and durable felt tournament players rely on. A dependable Penn choice for practice, league or match play on any surface. Full case of Penn Marathon (Extra Duty) tennis balls: 24 tubes (72 pressurized balls). Premium extra-duty felt and a durable core deliver extended play and consistent bounce. Perfect for clubs, academies and frequent players.