What do the Sixers lose with Sam Cassell’s departure? ‘He’s a brilliant basketball mind’

As Tyrese Maxey answered questions following the 76ers’ Game 2 playoff victory over the Brooklyn Nets, Sam Cassell unexpectedly entered the room through a door that connects to the coaches’ offices. And instead of discreetly slinking away, Cassell began pumping his fist into the air and chanting “Maxey! Maxey!”

“My protegé, Tyrese Maxey!” Cassell hollered while turning a corner to head down a hallway.

“That man’s crazy,” Maxey playfully countered into the microphone.

That scene captures what the Sixers are losing as part of the ripple effect resulting from the coaching change as the team transitions from Doc Rivers to Nick Nurse. After three seasons in Philly, Cassell has reportedly agreed to join a Boston Celtics staff that needed to be replenished under head coach Joe Mazzulla.

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Cassell will assist a Celtics team bursting with roster talent, including All-NBA players Jayson Tatum and Jaylen Brown, but that disappointingly fell to the Miami Heat in the Eastern Conference finals. That this gig was long expected to go to Stephen Silas — the former Houston Rockets head coach and Boston native who will instead reportedly join Monty Williams’ Detroit Pistons staff — speaks to the reputation Cassell has established as an NBA coach. He has recently been in consideration for head-coaching jobs, including for the Rockets’ opening before Ime Udoka, the former Celtics had coach, was hired in April.

Cassell had spent most of the past decade as an assistant under Rivers, who joked a few months ago that Cassell “thinks he’s part of our family.” They initially linked at the end of Cassell’s playing career, winning a title together in Boston in 2008. But Rivers’ unlikeliness to coach next season — the Toronto Raptors job remains open following a lengthy search — meant Cassell needed a new boss for the first time since he began his coaching career as a Washington Wizards assistant from 2009-14.

“When trust and culture happens [within a team] is when I walk away,” Rivers said during the 2022-23 season. “I feel like, with Sam, you can walk away at any point and the right things are being said.”

Cassell’s blend of experience and boisterous personality has helped him build close individual relationships with players — especially guards.

He was always one of the last people on the floor following Sixers shootarounds, directing future Hall of Famer James Harden as he played one-on-one and drilled various shots and situations. Yet Cassell was perhaps most instrumental in developing Maxey through direct critiques and thoughtful conversations. Maxey is now on an All-Star trajectory entering his fourth NBA season, following his breakout 2021-22 campaign by ranking fifth in the NBA in three-point percentage (43.4%) and scoring a career-high 20.3 points per game this past season.

“I’m very, very hard on him, if y’all don’t know that by now,” Cassell said of Maxey during a rare media appearance in November. “I’m critical of him, really. I think the sky’s the limit for the kid, and if he continues to develop, he’ll be fine.

“He’s my least worry on this team. He’s a true professional, and it’s a blessing for me, personally, to have a guy like that to work with.”

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Rivers also said earlier this season that Cassell has taken “major leaps” in the strategy aspect of coaching. The evidence: When the Sixers’ staff split into meetings focused on offense and defense, Rivers said Cassell was the only coach besides him who attended both sessions “because he’s that valuable.”

“I wish people could just see the mind,” Rivers said ahead of the Sixers’ Game 5 against the Celtics “He’s a brilliant basketball mind.”

To Rivers, those qualities all add up to a future head coach. And though Cassell continues to wait for that opportunity, he has found his new destination for next season.

Now, it’s the Sixers’ turn to find an assistant who can fill a similar role.