The 6ft 8in Flagg became the first freshman to be named Maine Player of the Year after leading high school Nokomis Regional to the state title in 2021.
He transferred to Montverde Academy in Florida, winning the 2022 USA Basketball Male Athlete of the Year and 2024 National High School Player of the Year awards.
He was part of the USA side that won the 2022 Under-17s World Cup and was named in the all-tournament team.
In 2024-25 Flagg averaged 19.2 points, 7.5 rebounds, and 4.2 assists in a 37-game debut season for Duke University.
They reached the Final Four and he was named National College Player of the Year.
Flagg, who made his debut for the Mavericks against the San Antonio Spurs in October, averages 17.5 points, 6.3 rebounds and 3.4 assists after 25 matches.