Back in early December, the Miami Heat were struggling. Erik Spoelstra’s squad had a record of 10-14 and was in the early throes a six-game Western Conference road trip. Worse yet, the Heat were beset by injuries. For the second game of the trip — a roadie against the Clippers in LA — Miami knew going in that it would be without three of five starters (Goran Dragic, Josh Richardson, and Hassan Whiteside), as well as two important bench players (Dion Waiters and Wayne Ellington); but things got even more dire when Tyler Johnson was injured early in the game.

Suddenly, Spoelstra only had eight players available to play, one of whom was Udonis Haslem, who at that point in the season had played a total of six minutes and who has played just six more in the nearly three months since he was forced into eight minutes’ worth of action on that early December night. When four of his eight available players found themselves in foul trouble, Spoelstra did something NBA coaches are typically loath to do: He turned to a zone defense.

“The first time we did it, we were down a lot of guys, so we were trying to save bodies and not get in foul trouble,” Heat guard Rodney McGruder says.

The gambit worked. The Clippers had blitzed the Heat for 62 points in the first half 28 in the third quarter but scuffled to eight points on just 2-of-15 shooting in the fourth quarter. The Clippers appeared flustered throughout, bricking from outside, driving to nowhere, and, crucially, drawing just three fouls after forcing 21 during the first three periods. The Heat, by contrast, were electric. Suddenly, the communication issues that plagued them through the early portion of the game were gone. Everyone was talking. Everyone was swarming. A thicket of limbs clogged up driving lanes. No matter where any Clipper went, a Heat defender or two was there waiting. And the Heat romped their way to a 23-point victory.

Spoelstra decided he liked the way the zone worked, and the Heat have used it extensively ever since. “It’s something that we’ve found that fits our identity and we don’t get away from what’s important to us,” he says.

Miami’s players are unsurprisingly tight-lipped about the specific tactics that inform their zone defense, but they do acknowledge that it’s designed mostly to wall off penetration and throw a wrench in the gears of opposing offenses.

“We’re just trying to not have easy blow-bys where guys can get into the paint and make easy sprays and stuff,” McGruder said. “Other teams just pass the ball around the zone. They don’t really try to penetrate it and get in the middle of the zone. Sometimes they’ll just pass it around and just shoot a 3. They play the way we want them to play.”

It’s working exactly as intended. Through March 2, the Heat played zone on 8.9 percent of their defensive possessions, according to Synergy Sports, and they allowed only 0.963 points per possession on those plays.

Miami has also used a couple of variations on its zone: they’ve mostly used a 2-3 with Whiteside, Bam Adebayo, or Kelly Olynyk in the back middle; but they’ve also toyed with a 3-2 with Richardson, James Johnson, or Derrick Jones Jr. up at the top.

“You have to be talking non-stop,” Jones says. “Because you don’t have a man so they are moving around, like, constantly. So, you have to just communicate non-stop so the rest of your teammates know where everyone is.”

Heat players figure that Spoelstra turns to the zone in order to get them talking. When he sees them getting lax with their communication in man defense, flipping to the zone forces everyone to speak up. If you don’t know where the help is or where you’re supposed to be forcing a man with the ball, it’s easy for an offense to break a zone. But when everyone’s chattering, it’s nearly as easy for a zone to break the offense.

“At first, a little shock,” James Johnson says, recalling the reaction from opposing offenses when the Heat first started using the zone on a consistent basis. “A little dumbfounded at first. I don’t think too many teams are putting in zone offense, you know? So now you have the coach writing plays on the fly or even doing plays that he normally does on man-to-man defense. So, I think it kind of discombobulated them a little bit, where they weren’t sure what to do and neither was the players.”

The Heat using a zone defense this often — and being as successful with it as they’ve been — would be a fascinating story in and of itself. But what makes it all the more interesting is that they’re not nearly alone in having taken the zone-defense plunge. In fact, they’re not even the heaviest adopters of zone this season. (That would be the Brooklyn Nets. More on them in a minute.) The league as a whole has already played over 500 more possessions of zone defense this year than it did during the 2016-17 and 2017-18 seasons combined.

During that three-year span, just ten teams have used a zone defense for more than 100 possessions in a given season. Six of those ten teams (the Heat, Nets, New York Knicks, Cleveland Cavaliers, San Antonio Spurs, and Toronto Raptors) are from the 2018-19 campaign; and it’s highly likely that by the end of the year, at least one and perhaps as many as three more teams will join that group.

It’s not all that difficult to figure out why the zone has swept through the league: It’s because it’s working. The aforementioned six teams, plus the Boston Celtics and Charlotte Hornets, have all used a zone on at least one percent of their defensive possessions this season, per Synergy’s tracking. Six of those eight squads have held their opponents to a worse field goal percentage in zone than in man, and for most of them, it’s by a not insignificant margin.

The Nets, as you can see above, have been nearly as effective with the zone as have the Heat. No wonder they’ve turned to the zone more often than any other team, with Kenny Atkinson becoming the first coach to use a zone for more than 500 possessions in any of the past five seasons.

“I like that we have it in our package,” Atkinson says. “To us, it’s not a gimmick. It’s something that’s in our package. It’s something we trust. It’s something we go to and we’ve used it heavily, quite honestly, in this last 20 to 30 game stretch. And we will continue to use it.”

It’s also not something Atkinson turned to out of nowhere.

“I’ve always wanted to use it,” he states. “We used it a little bit last year. It’s always been a thought of mine. And I’ve just had kind of more confidence with this group to use it. I think our length is something that helps us. We’re pretty long. I think it helps you limit fouling. I think it helps you keep the ball in front of you, keep teams away from the rim. You do give up more threes — which I detest — but that’s part of the deal. And I like the changing defenses. I think you can steal a game or two using it.”

The Nets have stolen more than that, rocketing themselves into the playoff race behind a defense that ranks in the top half in the NBA since an eight-game losing streak that dropped their record to 8-18 in early December (it was 21st before that) — a streak that was snapped just one day before the Heat trotted out their zone for its first extended run. The Nets had used theirs a bit early in the season, but have gone to it much more often since, and to great success. Brooklyn has allowed 0.979 points per possession in the zone, per Synergy, and it’s that performance that has led Atkinson to show so much confidence in returning to it.

The Nets also have variations on their zone. There’s a standard 2-3 where everyone is involved and talking, like with the Heat. But there’s also the one-man zone center Jarrett Allen will play on occasion.

“Normally our zone, coach just calls it whenever he feels is best for our defense,” Allen says. “And in terms of me playing the one-man zone … if they have somebody that can’t shoot, then normally I’m trying to help on the ball or something like that.”

When defending a non-shooter, Allen will spend entire stretches of the game not guarding his man, instead just “two-point-nine-ing” over and over again. (That’s when a big man stands in the lane for as close to three seconds as possible without being called for a violation, then darts out to reset the clock before jumping back in again and repeating the process.) It helps the Nets limit penetration because, well, Allen tends to be ridiculously difficult to score on at the rim. Many have tried him, and many — up to and including the King himself — have failed.

Allen is challenging 6.0 shots at the rim per game, according to Second Spectrum tracking data on NBA.com — a healthy figure, especially when you consider that he does not play as many minutes as the other top rim protectors in the NBA. Among the 108 players challenging at least three shots per game, Allen’s 56.8 percent conversion rate allowed ranks 28th, putting him in the top 25 percent of players and nearly on par with players like Rudy Gobert (55.5 percent) and Myles Turner (56.3 percent), who are among the favorites for Defensive Player of the Year.

Allen’s backup, Ed Davis, says the job Allen has in the Nets’ zone is incredibly difficult.

“The center on our zone has the toughest job because you’ve got to do so much moving around and you’ve got to stay out of the lane,” Ed Davis says. “You’ve got a lot of responsibilities and you’re out of rebounding position. So, it’s just a lot of movement going on.”

Brooklyn’s defensive rebounding has faltered in recent weeks (they’re now in the bottom third of the league in defensive rebound rate), but Atkinson doesn’t blame Allen for that. Instead, he notes that everyone else on the floor with him needs to pick up the slack, because the Nets need Allen to be out there patrolling the paint, deterring drives, and altering shots. It’s that exact scheme that has bred so much of their success.

Among the teams employing a significant amount of zone, none has seen more success with it than the Nets’ division rivals, the Toronto Raptors. Nick Nurse’s charges have allowed a paltry 0.870 points per possession with their zone defense this season, per Synergy’s tracking. That’s the second-best mark among the aforementioned 10 teams that have played at least 100 possessions of zone over the past three years.

“What I’m trying to do with it is a couple things,” Nurse says. “One is change rhythm of games. Two, usually it tends to limit pick-and-roll actions a little bit. And then on top of that, to protect your bigs, you don’t necessarily have to bring them up in the pick-and-rolls. So, you’re playing pick-and-rolls at the top with your zone, which is usually your wings and your guards, which I like. That’s part of the benefit of it.”

Toronto’s preferred zone is almost always a 3-2, and it almost always sees Nurse using the rangy, kinetic Pascal Siakam in the point position at the top of the key. Siakam’s combination of size, speed, length, athleticism, quickness, and instincts makes it nearly impossible for teams to get into their normal offense. Just try creating penetration with Siakam spreading his wings to encompass half the floor, plus two other strong defenders (any of Kyle Lowry, Danny Green, Kawhi Leonard, Fred VanVleet, or OG Anunoby) on the wing and in position to dig down on a dribble-drive.

“I just think that so many offenses in this league now, ours included, is four-out, drive-and-kick, and spacing. I think a lot of times you don’t need to chase people all over the place where you could stay on the same side of the floor and see it in a zone,” Nurse says. “Now, zones take a great deal of communication and a lot of polish. Our zone has been outstanding for us this year. I mean, outstanding. It really has. I don’t know the exact numbers but they’re pretty darn good. I see it as a chance to maybe if we need to, certain games, play bigger, and I see it as a chance to play a much more versatile offensive unit if the zone’s clicking.”

Nurse implied that after the acquisition of Marc Gasol, he’s willing to experiment with a 2-3 zone in addition to his preferred 3-2. Gasol brings a ton of experience as a defensive communicator and back-line backbone, and he should be able to pick up Toronto’s system on the fly. Being able to throw yet another look at opposing offenses could prove valuable in the playoffs, especially if that Raptors find themselves unable to generate stops at any point.

That hasn’t necessarily been an issue for them thus far this year, but it has for plenty of others. While the Heat, Nets, and Raptors have mostly employed their zones proactively, there are other teams who have turned to it as something of a last resort because their man-to-man defense has been so thoroughly shredded.

Such is the case with the New York Knicks, who just flat-out could not stop anybody when David Fizdale found himself turning to it out of sheer desperation in — wait for it — mid-December. Fizdale himself noted at the time that not many NBA teams use a zone and that it’s more of college defense, but that was okay because his young Knicks are essentially a college team anyway. (Minutes-weighted age pegs New York as the youngest team in the league this season and the seventh-youngest of the 3-point era, which encompasses the past 40 seasons.) The Knicks have waxed and waned on their zone usage since then, but Fizdale happens to like what it brings for his team.

“A lot of times it’s to throw a different look, just to change it up,” the bearded, bespectacled coach says. “Just depending on what the team is hurting you with. A lot of times the zone is just a way to change up the game a little bit. A few times that we’ve went to it this year, it’s helped us.”

Specifically, it seems to have helped rookie sensation Mitchell Robinson. Robinson did not play a single minute of college basketball last year, instead, dropping out of Western Kentucky in order to spend more time preparing for the NBA Draft. The Knicks snagged him at the beginning of the second round and he has leaped off the screen as a defensive force from Day 1. Robinson is blocking a completely ridiculous 10.4 percent of opponent two-point shots when on the floor, per Basketball-Reference, and he’s also blocked a flabbergasting 15 attempts from beyond the arc.

But for a large portion of the season, he didn’t really seem to know what he was doing out there on the floor, even while he was finding ways to make an impact anyway. But that’s to be expected for a guy whose last game action came against high-schoolers over a year ago. Using the zone for stretches simplified things a bit, as it gave Robinson a defined place to be on the floor, which in turn allowed him to utilize his incredible gifts on a more consistent basis — something now that’s carried over to the team’s man defense as he has begun figuring more and more things out over the past several weeks.

“When the coaches tell us what to do, it’s not hard to pay attention. I’m not looking to be out there lost. So, they kind of help me,” Robinson says. “I’ve really just got to be active. If I see a man starting to get by, I’ve got to be able to help a teammate out and be able to still close out to my guy.”

With the increasing prevalence of teams playing zone on defense, it follows that teams are also facing it more often when on offense. One of the teams that’s had zone played against them most is the Milwaukee Bucks. Only five teams have faced more possessions of zone defense this season, per Synergy, and given the rationale so many of the zone-heavy teams have employed for turning to a zone in the first place (improving communication and preventing dribble penetration), it’s not all that surprising. The Bucks, after all, have perhaps the league’s best penetrator in Giannis Antetokounmpo, who is averaging 8.4 points per game and shooting 64.4 percent on drives to the rim, per Second Spectrum tracking data on NBA.com.

The zone has been successful against the Bucks in some instances, but in others, they’ve found ways to get into the teeth of the defense and create openings for shots at the rim or from beyond the arc.

“We try and do a lot of the same things we do against man-to-man and not change too much,” Bucks coach Mike Budenholzer says. “One of our biggest things, man or zone, is we want to play fast. Hopefully off of misses, but even on makes, if we can get back and attack before the zone is set, that’s important. We want to continue to move, move the ball — not in the traditional zone, looking high-low or things like that — but move the ball, drive it, attack it, pick-and-roll it.”

Answers to the zone have been harder to find for teams that are not the Bucks, even if they’re strong offensive units. The Rockets, for example, have had zone played against them even more often than have the Bucks, the better to stop James Harden — possibly an even more dangerous driver than Antetokounmpo — from gaining access to the paint. But the Rockets, unlike the Bucks, have largely struggled when they’ve had a zone thrown at them. Only five of the league’s 30 teams have averaged fewer points per play against zone defenses this year, per Synergy, and the same applies to only two of the 18 that have played against a zone for at least 50 possessions.

For the most part, the performance of NBA offenses tasked with beating a zone defense this season has trended closer to the Rockets than to the Bucks. The league’s best coach, Gregg Popovich, has pushed his team into a zone for several extended stretches this season, and they’ve also worked against it offensively on multiple occasions. Prior to a recent game, Popovich remarked that he might even turn to a zone more often given the struggles of his team’s man defense, but he also allowed that a large part of the reason zones have been so successful this year is that, well, it’s just confounding for offenses to deal with.

“In general, NBA teams have no clue what to do when somebody plays a zone,” Popovich says. “The ball moves around the horn and after a while, somebody might attack a seam or do a little high-low or overload or something like that. But basically, the players get in mud. Doesn’t matter what team it is. They just get in mud. So, I think the zone might continue to be a bigger and bigger weapon for teams.”

For some teams, we’re already there. For others, it’s still a mere curiosity. And for others, it’s a non-starter. Amir Johnson laughed when approached in the 76ers’ locker room and asked about zone defenses. He stated firmly that the Sixers had not played it all year and would not be playing it anytime soon, either. (Synergy’s tracking bears this out. The Sixers are one of two teams to not play a single possession of zone defense this season.) But as we’ve detailed, the teams that are turning to zone are doing so with a good deal of success. For many of them, more success than with standard man-to-man, which continues to be the defense of choice for every team in basketball, even while we’re in the midst of the best offensive season in NBA history.

“Guys are so talented in this league,” Ed Davis says. “You can play the best defense possible and the guy still scores. So, you’ve just got to be creative.”