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The Philadelphia 76ers lost to the Boston Celtics in the Eastern Conference semifinals last month, and now they're losing a key assistant to Boston, too. Sam Cassell has agreed to join the Celtics' staff under head coach Joe Mazzulla, according to Shams Charania of The Athletic. Cassell will bring a veteran voice to Boston's bench, which is lead by the youngest coach in the league in Mazzulla. 

Cassell has been an assistant coach in the NBA since 2009. He spent the past three seasons under Doc Rivers in Philadelphia. Prior to that, he was an assistant with the Los Angeles Clippers (2014-2020) and Washington Wizards (2009 to 2014). He also played in the league from 1993 to 2009 and won three championships during his playing days, including one with Boston in 2008 -- when Rivers was the Celtics' head coach. 

Cassell has frequently been mentioned as a head coaching candidate, including for the Sixers' gig this offseason. They opted to go with Nick Nurse instead, and now Cassell will continue his coaching career in Boston, where he ended his playing career. 

Celtics legend Paul Pierce recently suggested that the Celtics bring Cassell in as an assistant under Mazzulla, and the front office obviously agreed. 

"You can't keep bringing in new voices. I'm going to add to what I got right now. I've got to add to it. It's already good. I've got to add to it. It's already there," Pierce said. "So, I'm bringing Mazzulla back but maybe I'm bringing in a veteran coach, like Sam Cassell. Some influence on the bench. Respect. A champion. Been a coach. Understands what it takes."  

Cassell is a well-respected assistant with ample experience, and he knows exactly what it takes to win in Boston, so the addition certainly seems like a sound one for the Celtics. Meanwhile, Nurse will likely look to bring in some of his own assistants in Philadelphia.