Kevin Durant and Russell Westbrook were curious. The former Oklahoma City Thunder teammates had a rare off night at home, and there was a college game nearby between Davidson and Oklahoma. Durant and Westbrook knew they needed to be there. They had to see Stephen Curry.

It was November 2008, only a few months after Davidson’s electric and improbable NCAA tournament run, and anyone who cared about basketball was mesmerized by Curry. Among the many people under Curry’s magical spell was a 10-year-old boy named Trae Young. He...