Mavericks rookie Cooper Flagg all business as he makes his professional debut at NBA Summer League LAS VEGAS (AP) — Cooper Flagg made his professional debut Thursday night in the NBA Summer League and celebrated an 87-85 win over Bronny James and the Los Angeles Lakers. Flagg finished with 10 points on 5-for-21 shooting, including 0 for 5 from 3-point range. He also had six rebounds, four assists, three steals and one block.