It wasn’t the time he tossed a pass to some fan in the first row because he thought one of his Dallas Mavericks teammates would be waiting.
It wasn’t even when he took a handoff and eventually laced his first career shot, a jumper from the top of the key.
It came early in the second quarter, when he held the ball on the left wing. Flagg was being guarded by last year’s Rookie of the Year, Spurs guard Stephon Castle, a hyper-athletic and active defender.
Flagg attempted a lazy pass that Castle deflected, and scooped, racing down the court for a transition layup. Flagg, rather than letting the mistake go, compounded it by committing a foul for an and-1 opportunity.
It was proof that the standards here would be different.
The highly-anticipated debut of the No. 1 overall selection was uneven — Flagg didn’t score his first points until the first possession of the second half — but, just like he did at Duke and just like he did in the preseason, he did the small things that can contribute to winning.
The Mavericks fell to the San Antonio Spurs, 125-92, but Flagg’s performance should nonetheless give Dallas plenty of optimism.
Though he started the game just 1-for-9 from the field, Flagg caught fire at the end of the third quarter, making three consecutive shots. He finished with 10 points.
He also hustled on defense and hauled in 10 rebounds for his first career double-double. He tried to push tempo up the floor. These are all traits the Mavericks will encourage Flagg to hone.
And for Dallas, which will be without star point guard Kyrie Irving for, at least, the majority of the regular season as he recovers from a torn ACL, it makes total sense to be patient.
The early portion of the season allows Flagg to get acclimated while the Mavericks face relatively low external expectations. It will allow Flagg to make mistakes, just like that second quarter turnover.
To prove that point, all Dallas needs to do is look to its opponent Wednesday night. San Antonio was deliberate with phenom Victor Wembanyama, putting him on a minutes restriction during his rookie season in 2023-24. The Spurs encouraged Wembanyama to bulk up and work on his body, to learn the speed of the NBA game.
Wembanyama dropped 40 points on 15-of-21 shooting (71.4%) Wednesday night and scooped up 15 rebounds. He might blossom into an MVP candidate as soon as this season and is already the odds-on favorite for Defensive Player of the Year.
Wembanyama and Flagg are very different players, so the progression won’t be exactly the same.
But Flagg won’t turn 19 until late December. He will likely learn something new every single game he plays early on.
That alone should have the Mavericks excited plenty.