Cooper Flagg’s Training Session with Jayson Tatum and Nick Sang: A Glimpse into a Future Celtic Star?

On September 6, 2025, Cooper Flagg, the No. 1 overall pick in the 2025 NBA Draft by the Dallas Mavericks, is set to train with Boston Celtics superstar Jayson Tatum and renowned trainer Nick Sang in Boston, sparking excitement among Celtics fans. The news, first reported by Bleacher Report and amplified by posts on X, has fueled speculation about Flagg’s future, with some fans proclaiming him a “future Celtic written all over him.” At just 18 years old, Flagg is already a generational talent, having dominated at Duke and impressed against NBA stars during Team USA scrimmages. This weekend’s workout with Tatum, a fellow Duke alum, and Sang, a respected skills coach, underscores Flagg’s relentless work ethic and raises questions about whether Boston could be his long-term destination. This article explores the significance of the training session, Flagg’s connection to Tatum, the role of Sang, and the implications for Flagg’s rookie season and beyond.

The Training Session: Context and Significance

The upcoming training session, scheduled for September 6-7, 2025, at a private facility in Boston, brings together three key figures in basketball: Cooper Flagg, Jayson Tatum, and Nick Sang. Flagg, fresh off his selection as the top pick by Dallas, is preparing for his rookie season, set to begin October 28, 2025, against the San Antonio Spurs. Tatum, a six-time All-Star and 2024 NBA champion, is sidelined for the 2025-26 season due to a torn Achilles suffered in the 2025 playoffs but remains a mentor to young players, particularly those from Duke. Nick Sang, a Boston-based trainer known for working with Tatum, Jaylen Brown, and other NBA stars, brings his expertise in skill development, focusing on footwork, shooting, and game IQ.

The session was first mentioned in a Bleacher Report article on September 3, 2025, which noted Flagg’s initiative to train with Tatum during the NBA’s pre-season window. X posts amplified the buzz, with one user stating, “Cooper Flagg training with JT and Nick Sang? He’s basically a Celtic already .” While Flagg is under contract with Dallas for $62.7 million through 2028, the connection to Tatum and Boston’s basketball ecosystem has sparked speculation about a future trade, especially given the Celtics’ need for a new star with Tatum injured and recent roster changes, including trades of Jrue Holiday and Kristaps Porzingis.

Cooper Flagg: The Generational Talent

Cooper Flagg, born December 21, 2006, in Newport, Maine, has been a basketball prodigy since his high school days. After leading Nokomis Regional High School to a state title as a freshman, he transferred to Montverde Academy, where he won multiple national player of the year honors. Ranked as the top recruit in the 2024 class, Flagg enrolled at Duke, where his freshman season was historic. He averaged 19.2 points, 7.5 rebounds, 4.2 assists, 1.4 steals, and 1.4 blocks on 48/84/39 shooting splits, earning the 2025 Naismith National Player of the Year and Wooden Award as a freshman, joining Kevin Durant, Anthony Davis, and Zion Williamson as the only freshmen to achieve this feat.

Flagg’s performance against Team USA in July 2024, where he outshined stars like LeBron James and Anthony Davis in scrimmages, solidified his status as the No. 1 pick. At 6-foot-9 and 205 pounds, Flagg combines elite defensive versatility with offensive potential, drawing comparisons to Tatum, Scottie Pippen, and Kawhi Leonard. His Summer League debut in July 2025, while inefficient (8 points on 3-of-12 shooting), showcased his poise, aggression, and defensive prowess, with The Guardian calling him “the most complete 18-year-old prospect since LeBron James.”

Jayson Tatum’s Mentorship and Duke Connection

Jayson Tatum, a fellow Duke one-and-done star, has been a vocal supporter of Flagg. Drafted No. 3 overall by the Celtics in 2017, Tatum averaged 16.8 points as a freshman before blossoming into a six-time All-Star and four-time All-NBA First Team honoree. His 2024 championship with Boston cemented his status as one of the NBA’s elite, though his Achilles injury in May 2025 has sidelined him for the upcoming season. Despite this, Tatum remains active in mentoring young players, particularly Flagg, whom he first met at his JT Elite Camp in 2023.

Tatum’s praise for Flagg has been consistent. In a March 2025 appearance on the New Heights podcast, he said, “The first impression I had of Coop was just how hard he played, how he competed… He plays the right way.” Tatum noted Flagg’s defensive tenacity and team-oriented play, qualities that mirror his own game. Their shared Duke connection, under coach Jon Scheyer, strengthens their bond. Flagg has cited Tatum as his favorite player growing up, telling ESPN’s Scott Van Pelt in June 2025, “Maybe Jayson Tatum. That’s somebody I watched a lot at Duke and then watched again as he went on to the Celtics.”

The training session with Tatum is a natural extension of this mentorship. While Tatum can’t participate physically due to his injury, his presence offers Flagg insights into leadership, preparation, and navigating the NBA as a high-profile rookie. Tatum’s advice to Flagg during a January 2025 Brotherhood Podcast episode—to “stay present” and enjoy the college experience—resonates as Flagg transitions to the pros.

Nick Sang’s Role in Skill Development

Nick Sang, a Boston-based trainer, is a key figure in this training session. Known for his work with Tatum, Jaylen Brown, Marcus Smart, and other Celtics, Sang specializes in refining footwork, shooting mechanics, and basketball IQ. His sessions emphasize game-like scenarios, helping players translate skills to high-pressure situations. A 2025 Boston Globe profile described Sang as “a master of breaking down complex moves into teachable steps,” noting his ability to connect with players through personalized drills.

For Flagg, training with Sang offers an opportunity to polish his offensive game, particularly his three-point shooting, which remains a work in progress (38.5% at Duke but inconsistent in Summer League). Sang’s experience with Tatum, who improved his three-point shooting from 34.3% as a rookie to 37.5% in 2024-25, could help Flagg develop consistency from deep. Additionally, Sang’s defensive drills, tailored to versatile wings, align with Flagg’s strength as a two-way player, capable of guarding multiple positions.

Why Boston? The Celtics Speculation

The choice of Boston as the training location, coupled with Tatum’s involvement, has fueled speculation about Flagg’s future with the Celtics. Posts on X, such as one from @celticsfanatic stating, “Flagg with JT and Sang in Boston? He’s coming home one day ” reflect the fanbase’s excitement. Boston’s roster is in flux after a tumultuous offseason, with Tatum’s injury, Holiday’s trade to Orlando, and Porzingis’ departure to Dallas. The Celtics, still a contender with Jaylen Brown and Derrick White, lack a young star to pair with Brown long-term, making Flagg an ideal target.

A May 2025 report by NESN floated a hypothetical trade where Boston could pursue Flagg, leveraging Brown and draft picks to acquire the No. 1 pick from Dallas. While speculative, the idea gained traction after Flagg’s Maine roots and admiration for Tatum were highlighted. Flagg grew up a Celtics fan, modeling his game after Tatum and Larry Bird, per NBA.com. A trade is unlikely in the near term, as Dallas views Flagg as their post-Luka Dončić cornerstone following Dončić’s trade to the Lakers. However, Flagg’s $359 million supermax eligibility in 2029 could make him a free-agent target for Boston if he doesn’t re-sign with Dallas.

Implications for Flagg’s Rookie Season

The training session with Tatum and Sang is a critical step in Flagg’s preparation for his rookie season. Facing a Dallas roster with Kyrie Irving, Anthony Davis, and Dereck Lively II, Flagg is expected to start at small forward, averaging around 15 points and 6 rebounds, per CBS Sports projections. The Mavericks, coming off a 50-win season but a second-round playoff loss, see Flagg as a two-way force to elevate their defense, which ranked 20th in 2024-25. His work with Sang could refine his offensive efficiency, addressing Summer League struggles where he shot 25% from three.

Tatum’s mentorship offers intangible benefits, such as handling the pressure of being a No. 1 pick. Flagg’s mental toughness, praised by The Athletic as “relentless aggression on both ends,” will be tested in Dallas, where fans expect him to fill Dončić’s void. The session could also expose Flagg to Boston’s championship culture, potentially influencing his long-term aspirations.

Fan and Media Buzz

The training session has generated significant buzz. X posts from Celtics fans, like “Flagg training with JT in Boston is destiny ” reflect optimism about a future connection. Media outlets have echoed this sentiment, with Sports Illustrated noting, “Flagg’s workout with Tatum could be a preview of a Celtics star in the making.” However, ESPN’s Tim Bontemps cautioned, “Flagg’s locked in with Dallas for now, but Boston’s interest is worth watching.” The narrative of Flagg as a “future Celtic” is fueled by his New England roots and Tatum’s endorsement, though Dallas remains committed to building around him.

Cooper Flagg’s training session with Jayson Tatum and Nick Sang on September 6-7, 2025, is more than a pre-season workout—it’s a convergence of talent, mentorship, and speculation about his NBA future. At 18, Flagg is already a generational prospect, with his Duke dominance and Team USA performances setting sky-high expectations for his rookie season with Dallas. Training with Tatum, a Duke alum and Celtics star, offers Flagg invaluable insights, while Sang’s expertise could elevate his offensive game. The Boston setting and Flagg’s admiration for Tatum have sparked dreams of a Celtics future, though his immediate path lies with the Mavericks. As Flagg prepares for his October 2025 debut, this weekend’s session underscores his work ethic and potential to become one of the NBA’s next great stars, whether in Dallas, Boston, or beyond.