INDIANAPOLIS — Jaylen Brown calls it “Celtic University.” Joe Mazzulla said a radical roster transformation during the offseason forced his team to place a bigger emphasis on basketball education.

Payton Pritchard can feel the shift during film sessions, when Mazzulla used to lash out more at his players, but now takes a more measured approach to his instruction.

“Now,” Pritchard said, “it’s more teaching. It’s not just getting on guys. Obviously, there’s times he’ll get onto us, but it’s just like we keep learning as we go and keep getting better and better in certain situations.”

How much has Boston learned already? After starting the regular season with three straight losses, Mazzulla’s team has climbed to third place in the Eastern Conference at 19-11. By beating the Indiana Pacers 140-122 on Friday, the Celtics won for the 14th time in their last 18 games.

As much as they have ridden the strong play of returners like Pritchard, Brown and Derrick White, that type of success has only been possible because the team’s inexperienced supporting cast has grown up quickly.

From the start, Mazzulla understood the importance of speeding up his team’s basketball development. It wasn’t difficult to identify the challenge ahead of him when the Celtics parted ways with much of their rotation over the offseason. The Celtics were saying goodbye to several former All-Stars who had played significant roles in the 2024 championship run.

For as much as the team would need to replace in pure basketball ability, Mazzulla recognized the need to make up for far more than just that.

“Everyone looks at the talent that we lost,” Mazzulla said, “but we lost cerebral (players), we lost mindset, we lost continuity. And, so, how quickly can you replicate that as fast as possible?”

In an attempt to solve the problem, Mazzulla decided the Celtics would need to change parts of their daily approach. No longer able to rely on a veteran-laden supporting cast, they would need to accelerate the learning process for their young players, many of whom had never logged significant NBA minutes.

Mazzulla couldn’t just snap his fingers and produce another Jrue Holiday or Al Horford. Still, day by day, the coach could do more to develop his team’s collective basketball IQ.

“I think that was the number one point of emphasis this offseason,” Mazzulla said. “After losing all that experience that we had, all that continuity that we had, just creating a better learning environment throughout the building, creating a better learning environment in the film room, on the road.

“Just different ways to make sure that our language and system philosophies are getting across. At the same time, guys are able to retain information at a fast level so that we can get to the best version of ourselves as fast as we can to get better.”

The Celtics believe they have not yet produced their best version. Still, 30 games into the regular season, they boast the Eastern Conference’s top net rating (plus-7.0), which ranks fourth in the NBA.