May 16, 2025; New York, New York, USA; Boston Celtics head coach Joe Mazzulla coaches against the New York Knicks during the first quarter of game six in the second round of the 2025 NBA Playoffs at Madison Square Garden. Mandatory Credit: Brad Penner-Imagn Images Brad Penner-Imagn Images

Celtics' Joe Mazzulla in 'Prove-It' Year Despite Extension, Says Insider

Originally posted on Boston Celtics on SI | By Ryan Stano | Last updated Sep 3, 2025 4:00 PM ET

The Boston Celtics decided to keep Joe Mazzulla in Boston for the long haul by signing him to a contract extension. They wanted to keep a coach who won a title with Boston.

Mazzulla was thrust into a tough spot when Ime Udoka was suddenly fired. He moved from being an assistant coach to being the man that all of the players were looking to for direction.

Despite the extension, one insider believes that Mazzulla is in a make-or-break year. He believes that he needs to prove that he can coach a team without its best player.

More news: Do Celtics Want to Quietly Tank This Year? Insider Weighs In

Celtics insider doesn't believe that Mazzulla has earned his extension yet

According to Chris Forsberg of NBC Sports, he believes that Mazzulla still has a lot to prove.

"Now, with a much different roster and without the team's MVP, I want to see what Joe can do with a squad with lower expectations and less talent. He has the extension in hand, but this is the prove-it year for Joe Mazzulla to show he is a top-tier coach in the NBA."

The Celtics clearly believe in what Mazzulla has done already with the Celtics, even though he had a lot of good players when he was able to win the title.

Coaching this team is going to be a lot harder to do without Jayson Tatum available for the year because of his torn Achilles tendon. Boston will have to find guys to replace his production.

More news: Celtics Praised By Insider for Controversial Offseason Decision

The Celtics will learn how good Joe Mazzulla is this year

If the Celtics do end up competing for a playoff spot and making some noise, Mazzulla will earn a lot of credit for that. He has to find ways to keep the offense at the same level as they have been.

Mazzulla will need to get Payton Pritchard highly involved in the offense as the new starting point guard. He is going to be shooting a lot of 3's to make up for the loss in volume from Tatum.

If the Celtics are able to make the playoffs, there is no doubt that Boston made the right decision to hand him an extension. The players clearly respond positively to what he tells them.