Among those around the Boston Celtics for the last few seasons, there has been an ongoing debate: Who is the team’s best defender?

Avery Bradley always received the accolades, making NBA All-Defense teams and earning effusive praise from guards around the NBA for his blanketing defense. He was the marksman tasked with locking down the opposing team’s elite ball handler and did it better than just about anyone in basketball.

Two years ago, Jae Crowder was viewed as the ultimate evolution of the three-and-D wing. He was tracking and smothering any wing, from quick perimeter scorers to freakish physical specimens like LeBron James, while holding down the block against bigs. His defense fell off last season when he took a bigger role in the offense and dealt with some nagging injuries that hurt his conditioning.

Then there’s Marcus Smart, the rare guard who can (and has) guarded all five positions with ferocity and control. Smart took over for Crowder last season as the team’s free safety and switching maestro, allowing the Celtics to lay the foundation for the switch-heavy defensive scheme they want to employ this season. Smart is leaner and lighter. With better conditioning comes better consistency, something he fell just short on when compared to Bradley.

“I’m definitely taking on a lot more responsibility without Avery and without Jae,” Smart said. “I’ve been doing it my whole life. I love playing defense, so it’s nothing new to me.”

Because of the revamped roster, the Celtics are very much working out the kinks of their defensive scheme in training camp right now. Pick-and-roll defense is all about early communication, allowing the matchup handoff to go smoothly without falling behind the ball. So far, that hasn’t been going quite up to head coach Stevens’ standards.

“I just think you look at the guys we lost and you look at the end of games, the ability to switch, and the ability to be impactful on the ball defensively, we’ve got guys that have a good understanding and a good savvy and a way about them that are helping each other,” Stevens said. “We are late because of lack of communication, but it’s not because of lack of effort, right now.”

In addition to Smart, Stevens will look to Jaylen Brown to be another shutdown defender down the stretch of games – although Brown still has plenty of learning ahead of him.

“I think then when the game boils down to it and people isolate more late, you gotta have guys that are going stop people one-on-one,” Stevens said. “That’s easier said than done and [Brown] had his moments last year when he was really good at it and he had his moments when he was still late learning the game in the NBA.”

Smart believes Brown is ready to step into his share of the role, and display with the energy and effort that is required to be a consistently great defender.

“Jaylen, his athleticism and his ability to guard perimeter guys and move with the smaller guard, he’s really athletic and he can be a great defender,” Smart said. “It’s just all about wanting to when it comes to defense. Anybody can play offense, but it takes a lot to get down and guard somebody for 24 seconds and then come back down and do it again possession after possession. And Jaylen has that ability.”

Targeted defensive assignments prove crucial in crunch time, but the primary focus is building a system that works throughout the game. Smart echoed Stevens’ plans to go switch-heavy on screens, emphasizing that building effective communication with newcomer Kyrie Irving will be crucial to team’s success.

“That’s why there’s five people out there on the court. If you can’t trust the guy behind you, then that’s a problem,” Smart said. “You need to be able to know that when you do something that’s called, the guy behind you has your back and Brad’s always coached that, especially here and that’s something that we’ll try to keep enforcing.”

This was one of the main areas of improvement for Brown over the offseason, learning how to read a switching situation earlier and getting ahead of the play. Stevens is seeing the results already in training camp.

“You can see that he’s just more comfortable than he was at this time last year,” Stevens said of Brown. “I think one of the biggest challenges for the guys in their first through fourth year is these guys are still trying to work, to move on to that next role or whatever the case may be. It’s really sometimes just about doing what you do better, right? And I think he’s doing that. He’s making open shots. He’s doing a good job defensively.

“I still think nobody will be harder on him at that end than I will, because ultimately, I think that’s a huge, huge part of our team, what he does defensively for us.”

A big question has been who will start at the two and four, with Kyrie Irving, Gordon Hayward and Al Horford being the only mandatory starters on the team. With Marcus Morris’ availability in the air to start the season ahead of the verdict of his Phoenix assault trial, there’s a possibility both Smart and Brown will start. Brown can fit into the lineup just about anywhere, as he did much of last season as a rookie.

“Two through four are about all the same for me,” said Stevens. “So yeah, he’ll guard a lot of twos, he’ll guard some ones, he’ll switch onto fours. I think his versatility is a big reason why we think he’s going to be a great defender.”

Stevens has to lean on Smart and Brown heavily. They may be on their rookie contracts, but they are veterans on a team with 11 new faces – half of whom haven’t played an NBA game before. But Jayson Tatum is going to play and it’s likely Semi Ojeleye, Abdel Nader and Guerschon Yabusele will too.

“Hey, our biggest challenge might be expediting the learning curve for the guys that are 19 to 21,” Stevens said. “Some of those guys have to play for us. We’re in a position where a lot of the teams that have the guys that we got are playing older guys off the bench. We’re not. So ultimately, we gotta make sure that those guys have their learning curve expedited as soon as possible.”