The Boston Celtics looked to fortify Joe Mazzulla’s coaching staff this offseason and they wasted no time in checking that box off their to-do list.

The Athletic’s Shams Charania, who cited sources, reported Sunday night that longtime NBA assistant coach Sam Cassell will join Mazzulla’s staff for next season. Cassell spent the last 14 seasons as an assistant in the league and was on Doc Rivers’ staff for the past three campaigns with the Philadelphia 76ers.

Cassell gives the Celtics an NBA coach with playing experience. He played for 15 years in the league and ended his career with three NBA titles, including helping the Celtics win the championship in 2008.

Once Cassell’s playing career concluded, he jumped right into the coaching ranks. He spent five seasons on the sideline with the Washington Wizards before teaming up with Rivers for six seasons with the Los Angeles Clippers. With a lengthy coaching résumé, Rivers thought Cassell should have been a candidate for the several vacant head coaching jobs scattered around the league during the offseason.

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“He’s terrific,” Rivers said before Game 5 of the Eastern Conference semifinals against the Celtics. “He’s got an incredible basketball mind and I wish people could just see the mind. He’s a brilliant basketball mind. When we have our offensive meeting and our defensive meetings, Sam’s the only one that goes to both because he’s that valuable. And it’s great. I go to both and Sam goes to both. … He deserves it.”

Mazzulla’s performance at the helm came under plenty of scrutiny in the playoffs, including some members of the media calling for his job. But with Celtics president of basketball operations Brad Stevens backing Mazzulla, Stevens hopes to give Mazzulla more support from the bench.

Bringing in Cassell will also offset the departure of several other assistants who are on their way to join Ime Udoka’s staff with the Houston Rockets.

Featured image via Mark J. Rebilas/USA TODAY Sports Images