DALLAS — Cooper Flagg looked different on the first day of training camp, and not only because of the 23 pounds he gained over the summer. It was the way he strutted around the gymnasium, shaking hands with every teammate, coach and executive he could and dapping up members of the media. It’s a contrast from last year, when Flagg was a rookie trying to fit in on a team centered around future ...

Cooper Flagg of the Dallas Mavericks poses for portraits at Mavericks Media Day at American Airlines Center on Sept. 25, 2026, in Dallas.

Stacy Revere/Getty Images North America/TNS

DALLAS — Cooper Flagg looked different on the first day of training camp, and not only because of the 23 pounds he gained over the summer.

It was the way he strutted around the gymnasium, shaking hands with every teammate, coach and executive he could and dapping up members of the media.

It’s a contrast from last year, when Flagg was a rookie trying to fit in on a team centered around future NBA Hall of Famers Kyrie Irving, Anthony Davis and Klay Thompson. This year, it’s Flagg’s team. Even the historic locker inside American Airlines Center that once belonged to Davis, Luka Doncic and Mavericks legend Dirk Nowitzki is now Flagg’s.

After a historic rookie season, he’s trusting an offseason plan to help him reach even greater heights in Year Two, which begins Wednesday in Houston.

“I’ve been working on a lot of different things, but just keeping it simple at the same time,” Flagg said. “I just have a lot of confidence right now in everything.”

Transformation: body and game

Despite being at the top of opponents’ scouting reports last season, the 19-year-old averaged 21 points, 6.7 rebounds, 4.5 assists, 1.2 steals and nearly 1.0 block in 70 games. It would seem hard to top a season in which Flagg led the Mavericks in total points, rebounds, assists and steals – the first rookie to do so for his team since Michael Jordan – but Matt MacKenzie, Flagg’s longtime trainer, said he thinks the forward has only scratched the surface of his potential.

“I just think you're going to see a more confident, more decisive version of Cooper on the offensive end,” MacKenzie told The Dallas Morning News.

One reason? The way Flagg transformed his body, part of the pair’s targeted plan for his offseason. MacKenzie first noticed last month when the Mavericks convened in Los Angeles for their minicamp.

“He wore a cutoff tank top, and it was the first time that I'd ever seen him really rock one of those,” MacKenzie said.

“They were in the weight room and I'm like, ‘All right, Coop, your shoulders are really starting to kind of fill out.' Normally you always see Coop in a T-shirt. So he's not really showing it as much, but yeah, he's noticeably stronger.”

He entered the NBA as a slender 18-year-old, listed at 6-9 and 205 pounds ahead of last season’s training camp. Flagg has since added 23 pounds, bulking up to 228. He also said he’s grown an inch, to 6-10 without shoes.

The added muscle was intentional, MacKenzie said, to help him absorb contact, maintain good balance and use his body to create advantages and separation between defenders.

“It just helps me be well-rounded,” Flagg said. “Adding on strength obviously can help create space and get to spots. I don’t think there’s any areas where adding strength can hurt you so I’m excited.”

MacKenzie said the Mavericks’ strength and conditioning staff, led by Geoff Puls, played a key role in this area. He also practiced yoga to help improve his balance, flexibility and strength, which he’s looking forward to testing once the season begins.

“Obviously, with him being only 19 years old, he will continue every single year to get stronger and stronger from a physique standpoint,” MacKenzie said.

Flagg began the offseason using his newfound downtime to rest his body and the left ankle he sprained in the Mavericks’ season-ending win over Chicago. The 2025-26 Rookie of the Year took three full weeks away from the court.

After the two-week mark, Flagg sat down with MacKenzie to start a deep dive of his historic rookie season. With Puls, they created a comprehensive development plan that could help him reach greater heights in Year Two. They used film and data to prioritize four areas of growth for Flagg:

— A better understanding of defensive coverages

— Tightening his handle

— Identifying different sweet spots and ways he could create space to get there

— Maintaining confidence and decisiveness with his outside shot

MacKenzie saw the fruits of Flagg’s offseason labor pay off several times during the first preseason game in Macao, notably at the 6:34 mark of the second quarter, when he executed all four of those lessons in one possession.

— Flagg was on the left side of the floor when he threw a pass toward the right wing to Tarik Biberovic, who took one dribble and delivered the ball back to his teammate. He took one dribble to the left, bringing his defender Tari Eason and weakside helper Kevin Durant along with him.

— He then dribbled behind his back toward his right hand.

— He rose for a midrange jumper at the left elbow of the free-throw line.

— Eason had a strong contest, but Flagg was already in his shot motion and sank the bucket.

“Just being able to see him in a very limited amount of time, being able to get to that shot, was very telling in just his decision-making, his processing, and being just more certain in terms of where he wants to go,” MacKenzie said.

Flagg’s summer wasn’t about rebuilding the wheel, but about refining his skills. Shooting 29.5% from 3-point range last season wasn’t a reason to hit the panic button. MacKenzie said he’ll naturally improve from beyond the arc with repetition and No. 4: confidence and decisiveness.

“I didn’t want to change anything huge in my shot,” Flagg told The News. “Obviously, there’s a lot of real things that you can tweak and change and mess with to figure out whatever works for you, but my base and everything is mostly the same.”

Committing to the plan

Flagg’s first NBA offseason took him from Dallas to Maine to LA to Durham, N.C., among other stops.

But no matter where he was or what he was doing, he was at a facility by 8 a.m. to get treatment and on the court by 9 a.m. He’d conclude his workout in the weight room, a place MacKenzie said he fell in love with this summer.

“He loves to compete. He loves to work out. There’s no time we’ve been in here where Cooper is not here,” Mavericks president Masai Ujiri said on media day.

After spending time with Flagg and his family through the offseason, including a visit to his annual basketball camp at the University of Maine, Ujiri said he feels even more of a responsibility to put him in a position to succeed.

“For a 19-year-old to think like this guy, to play like this guy, I think the sky is the limit, and it's a generational talent that we’re blessed to have,” Ujiri said.

Upon his hiring, Ujiri decided to move on from head coach Jason Kidd. He gauged the interest of Flagg’s former college coach, Jon Scheyer, before hiring Dusty May. The team president also overhauled the front office and traded several players, including Ryan Nembhard, a friend of Flagg’s.

“You learn really quickly how much of a business it really is,” Flagg told The News. “And the bad part of it is people you get close to and build relationships with, they get moved on from, like Ryan. Me and him had a great relationship. It’s tough, but you learn it’s a business.”

The changes around the Mavericks were a clear indication of their desire to build a contender around Flagg. He did his part during the offseason to make sure he has the physical and mental capacity to lead this team into the future.

“I think just taking that confidence from this summer into the season and just staying in that confident, aggressive mindframe is going to help me to get off to a good start,” he said.

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