Marcus Smart did not see the floor in Sunday’s Celtics-Wizards game. But for a few minutes in the fourth quarter, the former Boston guard was the center of attention.

With the Celtics breezing toward a 124-90 win over last-place Washington, fans at TD Garden began chanting “We want Marcus” — an unsuccessful plea for Wizards head coach Brian Keefe to sub in Smart, who dressed for the game.

Then, while these chants were echoing around the arena, a shouting match broke out between Smart and a fan seated behind the Wizards’ bench. Smart had to be restrained by teammates while he accosted the fan, whom he said “just crossed the line” with his in-game jeers.

“And we all know I don’t do line-crossing,” Smart said postgame. “And that was it. We move on. Unfortunate. You never want to see that, especially for a guy who’s coming back and who’s given this city everything he has. But it is what it is. Take the spirit, we’ll take it, on to the next one.”

The fan was escorted away from his seat by stadium security.

“(I was) just trying to get him out before it escalated more than what it was,” Smart said. “But that’s over with, it’s done with. On to the next one.”

Sunday’s game was the third trip back to Boston for Smart, who made two during his season-and-a-half with the Memphis Grizzlies. After nine seasons with the Celtics, Smart was traded to Memphis in June 2023 (as part of the trade that brought Kristaps Porzingis to Boston), then shipped to tanking Washington in February.

Two years ago, he was a starter on a championship contender (the Celtics reached five Eastern Conference finals and one NBA Finals during Smart’s tenure). Now, he’s a backup on one of the worst teams in basketball, asked to contribute less as a player and more as a mentor to the Wizards’ young roster.

Keefe said Smart has been a “terrific” addition, calling him a “tremendous leader (and a) tremendous player.”

“I’ve got to get used to that,” the 31-year-old Smart said of being one of the elder statesmen on an inexperienced, rebuilding team. “They’re calling me unc and things like that. I ain’t ready for that. But it’s great. It’s a great group of young guys here, and the thing that I love about them is they’re ready to learn and they’re willing to learn. They’re constantly asking me questions, constantly asking me to demonstrate things, and that’s what you ask for. As a competitor, as a player yourself, when guys come up to you, that’s a great feeling. It allows you to see that what you’re doing and the impact that you’ve made hasn’t gone unnoticed, and keep doing it. So I was very excited.”

Smart believes he still has something to offer on the court, however. He’s shot the ball well in his 15 games as a Wizard, posting small-sample field-goal and 3-point percentages (44.0% and 39.2%) that would be the best of his career.

“I’m one of probably the biggest competitors in this league,” Smart said. “As long as I’m able to be out there, I want to be out there and I’m going to be out there. Where, when, how – that’s not in my control. All I can do is control my preparation and be prepared for whatever is thrown at me. So obviously I would like to get back to that play of racking up those minutes and really getting out there with those guys, but like I said, control what I can control.”

As for being back at TD Garden? Smart said he’ll always enjoy that, regardless of what jersey he’s wearing.

“Flashbacks, baby,” Smart said, laughing, when asked about the fans chanting his name. “No, but it’s always great. The fans have always shown love, and it definitely brings back memories. I know my wife is over there, trying not to cry. It’s always a great feeling, but it definitely brought back some memories.”

Before speaking with the media postgame, Smart spent time catching up with old teammates in the Celtics’ locker room. He overlapped with most of Boston’s core players during his near-decade with the franchise, including Jayson Tatum, Jaylen Brown, Al Horford, Derrick White and Payton Pritchard.

“(I speak with them) quite actually often,” Smart said. “More than you would probably think. I try not to intrude too much, especially during the season, because I know everybody is busy, doing their thing. But we definitely keep in touch, and it’s always good to keep in touch with those guys. I grew up with those guys. We went through a lot of battles. Blood, sweat and tears. Everybody knows a few of those guys came to my mom’s funeral, so it’s a deeper bond than just basketball between us.”