EUC Penn Coach Tennis Balls Box of 18 For instruction, practice, and machine use. Penn Coach Tennis Balls are manufactured to the same specifications as Penn Extra-Duty Championship Balls, but due to minor cosmetic errors, are sold for a reduced price. What this means for you and your students is high-caliber play at a reduced cost. Expect great bounce, high reactivity, and consistent performance from these Penn practice tennis balls. Your students will quickly acclimate to the feel and pace of high-level play, allowing them to quickly bridge the gap between practice and match play. Optic Yellow color allows for excellent tracking. Optic Yellow Color