The KAP7 Size 5 COMP Water Polo Ball is the Official Ball Size for Boys 16&Under and 18&Under water polo. KAP7 has quickly become the go-to choice for amateur and elite water polo players alike. KAP7 has tapped into years of experience and proprietary technology to develop the COMP ball. The COMP ball has been designed to meet guidelines for local, national, and global specifications.