Our Plastic Baseballs are made from durable plastic with a hollow design. They are more durable than traditional plastic training baseballs. This durable construction combined with force-reducing holes, allows players to practice for hours on end without damaging the balls. These regulation size plastic hollow baseballs' circumference is 9-Inches. Safe for indoor and outdoor play. Great for practicing pitching, batting, throwing, and catching. These plastic balls also work perfectly for indoor pickleballs.