Ball played basketball for four years at Chino Hills High School in Chino Hills, California. As a freshman, he started alongside his older brother, Lonzo. Ball helped Chino Hills reach its first-ever CIF Southern Section Open Division championship game. Chino Hills fell in overtime to Centennial High School at the Southern California Regional Division I final. As a sophomore, Ball was teammates with his brother, Lonzo, and his cousin, Andre Ball. He suffered a foot injury before the season and missed a tournament at Fairfax High School in June 2014. On September 14, he scored 35 points with seven three-pointers to win the Ron Massey Memorial Fall Hoops Classic. In December 2014, Ball scored 53 points in a 111–80 win over Dorsey High School. At the end of the season, Ball was sidelined for four games with an ankle sprain but returned for the playoffs. His team lost at the CIF State Division I championship game. After the season, on April 21, he verbally committed to play college basketball for UCLA.