Mavericks hit with devastating blow right before Cooper Flagg era kicks off

In two days, the trajectory of Dallas Mavericks basketball will change forever as they will select Cooper Flagg with the No. 1 pick in the 2025 NBA Draft. This was the best outcome the Mavericks could have dreamed for this offseason after what happened last season, as Flagg looks like he will be an incredible player for Dallas on day one, but news on the Mavs' coaching front hasn't been filled with sunshine and rainbows this offseason.

Jason Kidd was in rumors involving the New York Knicks' head coaching job, and on Sunday, the Mavericks lost one of their lead assistants, Sean Sweeney, to the San Antonio Spurs. Sweeney had been a target of the Spurs for some time, and ESPN's Shams Charania made things official with a report yesterday afternoon.

Sweeney will become the associate head coach, the clear head assistant, in San Antonio alongside Mitch Johnson, one of the youngest head coaches in the NBA. The Mavericks have now lost multiple coaches ahead of next season, as Alex Jensen agreed to become the head coach of the University of Utah, and Sweeney joining Dallas' division rival will only make things tougher for the Mavs at the beginning of the Flagg era.

Mavericks lose Jason Kidd's lead assistant coach to Spurs

Not only will Sweeney have Kidd and the Mavericks' number, considering he has coached alongside Kidd for years, but Sweeney would have been the perfect coach for Flagg to learn under as he begins his NBA career.

In Dallas, Sweeney was known for helping guide young players as well as his elite defensive mind, and he would have been able to help Flagg in both of those areas. While Flagg's defense is expected to be elite off the bat, Sweeney would have helped him hone in on his defensive skills and adjust to the NBA quickly.

On top of that, Sweeney has been remarkable at helping young players be ready to contribute right away, with Dereck Lively II being a prime example of that. Lively II and Flagg share a bond already due to them both going to Duke, and if Sweeney were to have stayed, he likely would have spent some significant time working with Flagg.

As a member of the Mavericks' coaching staff, Sweeney was known for his incredible work ethic, next-level basketball mind, schemes on both ends of the floor, and skill to quickly develop players, and all of those attributes would have benefited Flagg tremendously as he steps into a new situation in Dallas.

While Flagg ultimately controls his own destiny, as he is one of the greatest prospects this game has ever seen in the last 20 years, having Sweeney by his side to guide him early on would have been game-changing. It was only a matter of time before Sweeney was offered an elevated role elsewhere, as he drew interest to become the next head coach of the Phoenix Suns, and Kidd and the Mavs have a big chair to fill when looking for their next lead assistant for next season.