On a second-quarter possession during their In-Season Tournament game against the Toronto Raptors last week, the Boston Celtics seemed to be in a defensive bind. Payton Pritchard, Boston's 6-foot-1 backup point guard, was matched up against Scottie Barnes, Toronto's 6-foot-9 point forward in the midst of a huge breakout campaign.If that matchup was a problem for the Celtics, though, the Raptors quickly bailed them out of it. Chris Boucher, who was being guarded by Jayson Tatum, came to screen for Barnes. The Celtics switched, and Barnes couldn't get anywhere isolating against Tatum up top. He wound up settling for a contested step-back three that grazed the front iron.While it's easy to say Barnes should've attacked the mismatch in front of him, that's not quite as easily done. Dribbling toward the basket from 25 feet out, with an ankle-biting pest ready to swipe at your high handle, would be tricky enough on its own. Trying to get there through a bramble of arms including Tatum's, Sam Hauser's, and Al Horford's - their wingspans measure 6-foot-9, 6-foot-10, and 7-foot-1, respectively - might feel like walking into a bear trap, even with Kristaps Porzingis and his 9-foot-5 standing reach parked on the bench.The Raptors could've found a way to capitalize on the advantage Boston seemingly gifted them - like, say, clearing out one side of the floor and having Barnes dribble into a post-up. But it's not always easy for an offense to change tack on the fly when it has a play call in mind and the floor is already configured in a particular way; teams probably don't spend a ton of time game-planning for such unconventional and uncommon matchups.Sowing that kind of confusion and indecision is very much part of Boston's defensive strategy, and it's why the Pritchard-on-Barnes matchup - sparingly deployed though it was - didn't come about by accident. There have been plenty of possessions this season in which Pritchard has been the primary defender of a gigantic offensive hub, be it Barnes or Julius Randle or even Joel Embiid. That looks as crazy as it sounds, but it's worked out for the Celtics more often than not. Pritchard's on-court defensive rating (103.5) currently leads the team.On this end-of-quarter possession against Philly last week, Pritchard started out guarding Embiid - this matchup didn't come about because of a switch - and the 76ers still couldn't get their act together in time to properly space the floor for a post-up. Embiid didn't even touch the ball: Your browser does not support the video tag. ESPNHere's another example from a recent game against New York: Your browser does not support the video tag. NBC SportsPritchard started out the possession on Isaiah Hartenstein, and the Knicks burned seven seconds of clock trying to get Hartenstein the ball on the block. When they finally gave up and swung the ball to the opposite side, Pritchard and Tatum exchanged places so the taller Tatum would be in low-help and rebounding position instead. The possession ended in a shot-clock violation.Pritchard's sporadic upsizing assignments are a small-scale extension of what Boston has been doing with Jrue Holiday, who is often the shortest Celtic on the floor but who spends big chunks of every game guarding the opponent's largest player and/or biggest interior scoring threat. While the 6-foot-4 Holiday jostles with players a half-foot taller than him, often fronting the post and working to deny entry feeds, the 7-foot-3 Porzingis usually camps out around the basket, lurking as a back-side help defender who can blot out the sun in an instant: Your browser does not support the video tag. BallyPorzingis will guard centers when they aren't shooting or rolling threats and are likely to be hanging out in the dunker spot, but otherwise he's more likely to be stashed on the least threatening opposing perimeter player. That particular tactic isn't new. The Celtics had Robert Williams III playing almost the exact same role the last two seasons, and NBA teams have dabbled in this kind of cross-matching ever since the Warriors hacked their second-round series against the Grit and Grind Grizzlies in 2015 by sticking Andrew Bogut on Tony Allen.These days, if there's a non-shooter on the floor, no matter what size, it's a decent bet that a center will nominally "guard" that player. By rejiggering their matchups in this fashion, defenses can keep their best rim-protectors hovering around the court's most valuable swath of real estate while simultaneously making opponents' 1-5 pick-and-roll actions a lot more switchable."Teams are much more willing to employ that kind of strategy now," Warriors defensive coordinator Ron Adams, who thought up that fateful defensive adjustment eight years ago, recently told CBS Sports' James Herbert. "By that I simply mean stranger matchups, not guarding certain people in an orthodox way. That's zoning up on them a little bit more. Protecting the basket. That kind of thing. I think it's pretty commonplace now."But nobody is doing it quite like these Celtics, who are taking those concepts to what feels like their logical endpoint. They fiddle with their matchups constantly, size disadvantages be damned, for the sake of disrupting their opponent's flow. Most defenses, when they cross-match their own center onto a non-shooting small, will use their next-biggest player to guard the opposing center. Boston is frequently doing so with its point guards. Again, that's not entirely unique to this season - Marcus Smart has spent time guarding bigs in the past, including Embiid for stretches in last year's playoffs - but extreme cross-matching has never been such a prominent or intentional part of the team's foundation. Pritchard has spent more time guarding Embiid in the teams' two matchups this season than Porzingis has. Holiday has guarded him more often than any Celtic other than Horford. The benefits of this tactic are manifold. Celtics coach Joe Mazzulla particularly likes the way it can reorient where opposing teams initiate their offense."I think ball pressure's important, high pickup points are important. And when you can get guys who pick up full court or pick up a couple feet behind the 3-point line, you can start your ball pressure and force teams to start their offense a little further out than they want to," Mazzulla told me. "Our guards have done a really good job of that, regardless of who they're guarding. They pick up full court, three-quarter court, 4 feet from the 3-point line, and that disrupts the offense."Interestingly, that ball-pressuring edict isn't leading to many takeaways; the Celtics' rank 28th in opponent turnover rate. The mistakes they're forcing are subtler and have more to do with taking teams' bread-and-butter actions off the table. Their cross-matching configurations allow them to comfortably switch any and all above-the-break actions and, if needed, to scram-switch on the back side. Opponents often aren't able to create meaningful advantages with their initial actions, so they're either forced to veer away from their preferred play triggers or stack more actions on top of each other and work deeper into the clock in order to find those advantages: Your browser does not support the video tag. BallyBoston forces opposing offenses to use up more time before a shot than all but two teams, per Inpredictable. "We're just trying to give teams different looks, and we're trying to have Jrue guard the most action and the most guys we possibly can," Porzingis explains. "A lot of times they put the 5 in some early action, some pick-and-rolls, he just switches and boom, he's on the ball-handler."It's not always perfect. Having to do all that switching while ensuring Porzingis remains the last line of defense can make it hard for everyone to keep track of their assignments. Gaps appear when the offense is swift and purposeful about stringing actions together: Your browser does not support the video tag. NBC Sports"We're still getting better because it can get a little bit chaotic as the offense goes on," Porzingis says. "But I think the more we play together, and the more we'll be in those situations, the quicker we'll react."Another benefit for the Celtics in having the smallest defender on the court guard a player the opposing team wants to run its offense through - whether as a post hub or a ball screener - is having that much more size and length in help position. Their scheme blends man and zone concepts and essentially scoffs at the very notion of primary assignments, knowing that solving modern offenses is much more a five-on-five equation than a one-on-one problem. With the amount of switching that goes on, and the amount of help involved in every action, those initial matchups have never been less fixed.Of course, this wouldn't work if the Celtics didn't have so many great helpers and switchable defenders elsewhere. Nor would it work if the guards they're using to cross-match weren't uniquely suited to the role. Holiday is a defensive unicorn and one of the strongest players in the game. Pritchard is short but stout; he weighs as much as Chet Holmgren. Derrick White is capable of sliding up multiple defensive positions as well, but more importantly, his elite point-of-attack containment allows Boston to shift Holiday onto opposing big men without downgrading their defense against top perimeter threats.Maybe that's why Mazzulla's advice for potential imitators is essentially to not try this at home. "It's just our personnel," he says. "It's because of our guards, their ability to guard multiple positions, their toughness, and their individual defense. I think (our scheme) highlights our guys' ability to do that, and their willingness to do that throughout the game."The NBA's cross-matching revolution has had many ripple effects. It's changed not only defensive but offensive strategy, and it's forced non-shooting guards and wings to become competent screen-and-rollers. It's also probably contributed in some part to the league-wide decline in rim attempts, with more and more 2-point shots getting nudged back into the upper paint. (Average rim frequency this season is the lowest it's been since 2004-05, per Cleaning the Glass, while short mid-range frequency is the highest of any season in its 21-year database.)The Celtics are on the cutting edge of that trend, and the results are undeniable. They're currently allowing the league's fifth-lowest rim-attempt rate (28.7%) and the lowest at-rim field-goal percentage (58.2%). That's the biggest reason they rank second in overall defensive efficiency outside of garbage time.Other teams may eventually get a better handle on how to attack them and their funky matchups, but for now, the Celtics are thriving with a unique approach that makes creative use of their malleable personnel.