One of the most popular questions about the 2019-20 Boston Celtics heading into the season is some version of “how will the defense look by swapping out Al Horford for Enes Kanter?” Sometimes, a less nice version of the question is asked more as a statement by saying, “the Celtics defense is going to be terrible with Kanter/without Horford.”

Let’s dive into some numbers!

Under Brad Stevens, Boston has consistently posted anywhere from solid to very good Defensive Ratings:

· 2013-14 – 107.7 – 18th

· 2014-15 – 104.5 – 12th

· 2015-16 – 103.6 – 4th

· 2016-17 – 108.4 – 13th

· 2017-18 – 103.9 – 1st

· 2018-19 – 107.8 – 7th

That first season is a bit of an anomaly. Boston had launched a full rebuild and their best players and defenders, Rajon Rondo and Avery Bradley, combined to play just 90 games. Every other year, the Celtics have been in the league’s top-half of defensive teams, and pretty regularly a very good defense.

The 2015-16 campaign might give us the best hint of what the 2019-20 Celtics could be. That 2016 team featured Avery Bradley as a member of the All-Defensive 1st Team. The rest of that group? Some scrappy overachievers, ground-bound big men and an undersized point guard. Sound familiar? Let’s look at who rounded out that roster:

· Rotation ball handlers – Isaiah Thomas, Marcus Smart

· Rotation wings – Avery Bradley, Jae Crowder, Evan Turner

· Rotation bigs – Amir Johnson, Jared Sullinger, Kelly Olynyk, Jonas Jerebko, Tyler Zeller

Outside of Bradley, Smart and maybe Crowder, no one from that group screams a high-level defender. The funny thing? The best individual Defensive Ratings (albeit a somewhat flawed metric) belonged to Sullinger, Johnson, Crowder and Olynyk. Even David Lee, who was waived shortly after the trade deadline because of his ineffectiveness, posted a solid Defensive Rating.

Why is this instructive? Let’s look at the current Celtics:

· Rotation ball handlers – Kemba Walker, Marcus Smart

· Rotation wings – Jayson Tatum, Jaylen Brown, Gordon Hayward, Semi Ojeleye

· Rotation bigs – Enes Kanter, Daniel Theis, Grant Williams, Vincent Poirier, Robert Williams

There are a lot of similarities there. Walker, like Thomas, is an undersized lead guard who will play a lot of minutes and carry a heavy offensive load. Like they did with Thomas, teams will try to isolate Walker and go at him. Walker is bigger and is a competitive defender, but he’s not making the All-Defensive Team anytime soon.

Walker being on the floor a lot (he’s averaged over 34 minutes per game for his career) is something the Celtics will have to scheme and work around. The good news is, they’ve done this with Thomas, and more recently Kyrie Irving, for years through jump-switches and switch-backs. Stevens and his staff know how to build a competitive defense with a small guard that opponents will look to attack.

Going further, Bradley’s All-Defensive prowess has been replaced by Smart’s long-overdue recognition. Smart may not start this season, but he’ll be on the floor during any important minutes when the team needs a stop.

On the wing, the combination of Tatum, Brown, Hayward and Ojeleye (who can and will swing to the bigs line when necessary), is at least as good as what the 2016 group offered. Tatum and Brown have already proven to be capable defenders in their short careers, and both took things to another level this summer while playing for Team USA. Hayward remains an underrated defender, who will fill the Turner role in a lot of ways as a big wing.

Photo by Matthew J. Lee/The Boston Globe via Getty Images

But it’s not really about the ball handlers or wings, is it? It’s about Horford being gone. And even more so, being replaced by Kanter. That’s where most of the angst comes from for Celtics fans, and it’s not misplaced comparing the two as individuals. Horford is one of the best defensive bigs in the game. He’s a game-changer, capable of defending inside and outside. He was the key to Boston’s “switch everything” defense the past few years.

Kanter’s reputation as a defender is one that presumes that teams will try to put him in as many pick and rolls as possible. A quick internet search will give you a host of highlights (lowlights?) of Kanter getting caught in no man’s land, as guards blow by him for layups and jumpers. Kanter is often stuck in the middle, neither defending the guard nor the roll man. Something to note: most of the highlights feature Kanter as a member of the Oklahoma City Thunder, where he was rarely asked to do anything defensively but sort of get in the way and rebound (more on that later), or they are clips from his time in New York when the Knicks were an abject disaster as a team on defense.

Back in 2016, there was no Al Horford; he wouldn’t come along until the next season, when Boston would curiously slip from 4th to 13th in Defensive Rating. Amir Johnson was criminally underrated as a defender during his time in Boston. Because he didn’t rack up blocks and steals or make many highlight plays, many overlooked his contributions. Johnson was asked to play a role of defensive big more than most realize, and he was asked to do so at a point where age had crept in and his once-terrific athleticism had waned.

And then you have players like Sullinger, Olynyk, Jerebko and Zeller. Combined, you can measure their vertical leaps and speed in terms of inches and minutes vs feet and seconds. Yet somehow, Boston put together the league’s 4th best defense. How did they do it?

First, they made it very simple for their relative limited cast of bigs. Boston did very little switching with the big men. Instead, they played what is commonly called a “drop” style of pick-and-roll defense. Our friends at Brew Hoop did a nice job articulating this style of defense, as it pertained to Brook Lopez. The general idea is to not switch, while dropping the big back to protect the basket. As you can see in the clips, Lopez has done quite well in this style of defense.

In this clip, Lopez is guarding a traditional big in Rudy Gobert. The Bucks ask Lopez to keep it simple. He never comes higher than the free throw line, then he drops back to the restricted area to protect the rim against Donovan Mitchell.

This clip shows Lopez guarding against a shooting big in Myles Turner. He starts a couple of steps above the line. Against a shooter like Turner, the Bucks ask Malcolm Brogdon to stick with the screener in case he pops, while Lopez again drops to protect against the drive.

Now, Kanter isn’t Lopez, who has become an underrated defender, but he’s capable of performing in a similar scheme. How do we know this? Because it’s exactly what the Portland Trail Blazers asked him to do during their Western Conference Finals run with them this past year.

Part of the above coverage in dictated by where the Thunder start the action. It’s inside the arc, so Kanter drops deep. If Dennis Schroder wants to take a mid-range pull-up, let him have that shot. Kanter is there to protect against the drive, while also being in position to recover to the rolling Steven Adams for the block.

Again, this action starts inside the arc. Kanter again drops to take away Gary Harris’ drive to hoop. And again, he recovers to contest Nikola Jokic taking a short floater.

Kanter doesn’t have great speed, but what he does have is decent short-area quickness. When he’s asked to drop and defend an area that has a diameter of 3-5 feet, Kanter is fine. He’s got fairly quick feet. A famous example of quick feet is this play from the 2016 NBA Finals when Kevin Love contained Stephen Curry, in part because Love has terrific short-area quickness. Curry never makes Love move more than a few feet on either touch. That allowed Love to stay with him and contest the shot. This is a prime example of what NBA coaches talk about when they talk short-area quickness.

To be fair, Boston won’t ask Kanter to guard Curry, or any other explosive scoring guard, around the arc. They’ll simply ask Kanter to drop and protect the paint in a small area where he can hold his own, while letting the guards and wings handle the perimeter.

Drop coverage is also an area where Vincent Poirier is best, as detailed by Max Carlin earlier this summer. It’s also how Daniel Theis has done his best defensive work in the NBA. Kanter, Poirier, and Theis all project to be the main centers for Boston.

What do the Celtics lose by utilizing this coverage? The main thing is Horford’s brilliance on the perimeter. Horford’s ability to execute switches and guard anyone from Ben Simmons to Giannis Antetokounmpo was a key for Stevens’ defensive schemes over the last few years. Boston doesn’t have anyone on the roster who is ready just yet to replicate that, minus maybe Ojeleye for spurts. Grant Williams should eventually help in this regard as well, but he recently admitted that defending on the perimeter has been his biggest adjustment so far. That means switching everything is largely out, as is tilting the defense towards a big ball handler. At least for now.

The wildcard is Timelord. Once he shows he truly grasps where to be on both ends of the floor, Robert Williams could do a respectable Horford imitation as a defender. He’s got the quickness and wingspan to contest on the perimeter. And his athletic gifts allow him to recover from a misstep or overplay to challenge shots. When Boston is facing a particular mobile opposing big, or a team like Milwaukee or Philadelphia who have big ball handlers, Williams might see additional run.

There is one area where Boston’s defense will certainly be improved: rebounding. As coaches like to say “the possession doesn’t end until you have the ball,” and securing rebounds has often been a challenge for the Celtics.

Over Stevens’ tenure in Boston, the team has never had an elite rebounder. For all of Horford’s gifts, he’s never been dominant on the glass, nor have any other Celtics bigs over the last half-decade:

· 2013-14 – 19th in defensive rebound rate

· 2014-15 – 14th

· 2015-16 – 26th

· 2016-17 – 27th

· 2017-18 – 11th

· 2018-19 – 17th

More than anything, this is where Kanter and Poirier excel. Kanter has been an excellent rebounder since entering the NBA. His defensive rebounds rates are generally between 20 and 30%. That rates right up there with the best rebounders during his time in the NBA. His overall numbers never hit the leaderboard, because Kanter rarely plays enough minutes to get there. But if you dig into the numbers, he’s regularly among the leaders when adjusted for minutes played. Poirier’s European numbers portend similar excellence on the boards.

Finally, this summer’s USA Basketball team at the FIBA World Cup featured big roles for four Celtics. In the games they played, Tatum, Brown and Smart were all regularly asked to defend much bigger players. Gregg Popovich went to Brown and Smart as his primary defenders against Gobert for a chunk of the USA-France game. Expect to see Stevens ask those three, along with Gordon Hayward, to defend bigger players on a regular basis. It’s also a way for Stevens to get his best five players (Tatum, Brown, Smart, Hayward and Walker) on the floor together for stretches of games.

Overall, Boston’s defense will be different this year. They aren’t going to switch everything, although they’ll continue to do that quite a bit, just not with the center. They’ll probably incorporate even more of their always excellent jump-switches and switch-backs to keep themselves in the best match up possible. But they won’t feature a big man defending alone in space very much, as they don’t have Horford to do that. The trade off could be more open jumpers for shooting bigs, but when those shots miss, the Celtics will be better positioned to rebound the ball than they have been in years. That alone should help keep Boston around the top-10 in overall defense, even if it looks different than it has for a few years.