For over a decade now, there has been a mystery that has flummoxed NBA coaches and analysts alike: How do the Boston Celtics defend three-pointers so well? Since the 2007-08 season, when the Celtics hung Banner 17, Boston has finished no lower than fifth in opponent three-point percentage. This is generally a statistic that fluctuates greatly from year to year. It’s not uncommon for a team to finish top-10 one season and drop to bottom-10 the next. For years, it’s largely been a statistic chalked up to luck, as opposed to an actual skill. If anything, the goal for most coaches has been to limit opponent three-point attempts vs. worrying about the actual percentage they allow.

But Boston has obviously figured something out. No one gets lucky for 11 straight years, not even the franchise that has a leprechaun at half court. CelticsBlog talked to coaches, players, scouts and analysts to get a sense of what the Celtics might be doing differently than anyone else at defending the game’s great equalizer. Through these conversations, and countless hours of film review, an incredible, but largely unnoticed theme surfaced: Boston does defend the arc differently from almost every other team. And the Celtics have undergone two different evolutions to sustain the unsustainable.

Defending the three-pointer has undergone a progression, just as taking the shot has. Shooting threes started as a novelty, with defenders treating it as such. You want to shoot from 30 feet away? Feel free. Watch tape from the 1980’s and 1990’s. Teams hardly worried about defending someone behind the arc.

As the game changed over the last twenty years, defenses did, too. You now had to protect the three-point line and teams still defend the three in a traditional way: run out on the shooter with a hand up.

In the summer of 2007, as Danny Ainge turned over the Celtics roster by adding Kevin Garnett, Ray Allen and a host of role-playing veterans, Doc Rivers made an addition of his own to the coaching staff. Rivers hired an assistant who was well-respected around the NBA, but largely unknown to the general public. Tom Thibodeau was brought to Boston to build a championship-level defense. From day one, Rivers called Thibodeau his defensive coordinator and handed him the reins.

Everyone remembers Kevin Garnett turning in a Defensive Player of the Year campaign. KG was all over the court that season while Thibodeau was quietly crafting a plan to revolutionize the way teams defended three-pointers. As three-point field goal attempts continued to creep up, Thibodeau knew the importance of defending them well. The 2008 Celtics famously built a defense that overloaded the strong side of the floor. That meant teams could get open looks if they reversed the ball quick enough. Opponents got up a modest number of shots from behind the arc, as the Boston allowed 18.7 three-point attempts per game. That figured ranked 19th in the NBA.

While they couldn’t exactly stop teams from bombing away at the arc, Boston could change how they defended those shots. The Celtics allowed teams to shoot just 31.6 percent on three-pointers, good for first in the league. But how did they pull that off? That’s where the story gets interesting.

Prior to the 2008 Celtics, teams had largely defended three-pointers in two ways. First, you do what you can to limit the attempts, especially for the best shooters in the game. If you faced a team that loved to let it fly, you extended your defense and tried to take those shots away. If you did surrender a long-range attempt, you got a hand up and turned to box out, as seen in the clip above. The concept of closing out hard on a shooter didn’t really exist, at least not like it does today. When it did, it was reserved for the game’s best marksmen and not your average shooter.

Thibodeau changed this for Boston in a subtle, but significant way. Because they played a style of overloading the strong side, the Celtics knew they would allow some weak side three-pointers. There wasn’t really a way to prevent it. So what Thibodeau did was ask his players to close hard on those shooters. Not just the good ones, but every shooter. And he asked them to do it by running hard at the player, hands up, directly at the chest of the shooter.

The idea was to throw them off their rhythm because of the oncoming pressure. With a defender charging directly at the shooter’s body, the shooter can become distracted, which throws off their normal shooting form. In the traditional way of defending a three-point shot, a hand up is no more distracting than 20,000 fans yelling and waving their arms might be to a shooter. Running at the shooter impacts their landing space and can throw off the entire rhythm of the shot.

As the numbers show, it worked.

Boston 3-point Defense Under Doc Rivers Season Opp 3FG% Rank Opp 3PA Rank DRtg Rank Season Opp 3FG% Rank Opp 3PA Rank DRtg Rank 2008 31.6% 1 18.7 19 1 2009 34.9% 5 17.7 13 2 2010 34.2% 4 16.8 5 5 2011 34.0% 5 15.9 2 2 2012 30.8% 1 16.9 4 1 2013 34.2% 4 19.9 13 7

Over the following five seasons under Rivers (two more with Thibodeau in the defensive coordinator role), Boston would finish no lower than fifth in opponent’s three-point percentage. They even got back to leading the league, as part of the NBA’s best overall defense in 2012. Several of the players from that era of the Celtics remember the emphasis on how to defend three-pointers being drilled over and over in practice.

Some of those players admit to being skeptical at the approach. One player said, “You have to understand, fouling a three-point shooter was the worst thing you could do. I mean, the worst! Every other coach I had would bench you in a second if you did that. In Boston, we had Thibs telling us to sprint at guys to the point of making contact. If you fouled, you fouled. I thought they were crazy, but man it worked.”

In 2013, facing the task of rebuilding, Rivers left town and Ainge stunned the basketball world by hiring Brad Stevens from Butler University. Stevens and his Bulldogs had captured the nation’s hearts with back-to-back runner-up finishes in the NCAA Tournament in 2010 and 2011. Helping them get there? You guessed it! Exceptional three-point defense.

Butler 3-point Defense Under Brad Stevens Season Opp 3FG% Rank Opp 3PA Rank Season Opp 3FG% Rank Opp 3PA Rank 2008 31.8% 31 31.7 84 2009 32.7% 78 34.9 239 2010 31.7% 60 31.6 130 2011 32.2% 51 35.5 254 2012 31.3% 42 33.4 193 2013 33.2% 133 30.4 83

Outside of his final season, when Butler was rebuilding their talent base following back-to-back Final Four appearances, the Bulldogs finished no lower than 78th in opponent’s three-point percentage. It’s important to remember that this is out of over 300 teams. Similar to the Celtics over the same period, Butler didn’t really limit three-point attempts. They just defended them better than most and more consistently than everyone.

Stevens headed to Boston to help rebuild the Celtics. In those early days, he continually stressed that he was focused on the process of improvement as opposed to results. But one trend carried over, both from the previous Boston regime and from Stevens’ Butler teams: three-point defense.

In five seasons under Stevens, the Celtics have finished fifth, fourth, fourth, second and first in opponent’s three-point percentage. During that same period, they’ve generally finished around the middle of the pack in attempts allowed.

Boston 3-point Defense Under Brad Stevens Season Opp 3FG% Rank Opp 3PA Rank DRtg Rank Season Opp 3FG% Rank Opp 3PA Rank DRtg Rank 2014 34.7% 5 18.9 4 18 2015 33.6% 4 22.0 10 12 2016 33.6% 4 23.3 11 4 2017 33.2% 2 27.0 14 13 2018 33.9% 1 27.7 9 1

As the three-pointer has taken on increased importance in the NBA, Boston has not only continued their success at defending them, they’ve improved. But they don’t do it the same way Thibs once taught his charges.

At Butler, Stevens was often working with unheralded players. This regularly resulted in a talent gap that needed some scheming and coaching to overachieve, especially at NCAA Tournament time. Just like he does in Boston, Stevens schemed with the best of them. But what set his teams apart defensively was their three-point defense and he brought those same principles with him to the Celtics.

On its face, Stevens’ three-point defense doesn’t appear to be different from Thibodeau’s. Both teach players to get out quickly to shooters as opposed to trying to eliminate three-pointers. But Stevens and crew have amped it up. Way up.

Remember the player who told us that fouling a three-point shooter was the worst thing you could do? How do coaches teach players to avoid that? Many still emphasize the idea of taking the shot away—if you can’t, just close with a hand up and turn to box out. Those who have adopted the Thibodeau-style, teach to run hard at the shooter, as discussed above.

However, what the Celtics do now is considered far too risky among many coaches. Boston teaches their players that if they can’t take the shot away, to wait for a split-second until the shooter starts his motion, then to fly out at them. Literally, to leave their feet in a manner similar to contesting a shot in the paint. Take a look:

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Jayson Tatum leaves his feet to contest this jumper from Tim Hardaway Jr. For most coaches, this is a major no-no. Because of Tatum’s length, they’d rather have him just run out with a hand up. Not Stevens and his staff. They want Tatum to put that length to an even greater use by getting all the way up in the shooter’s vision and making it as difficult an attempt as possible. And when they close, the Celtics want their defenders to close as tight to the shooters body as possible, to the point of even making slight contact as they land.

Here’s another example of Terry Rozier challenging Kevin Love:

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Rozier makes up for the size difference by full on leaping at Love to contest the jumper. If he just comes out with a hand up, Love uses his 7-8 inch height advantage to just shoot over the top of Rozier.

Now, this approach does end in a bad result sometimes like Tatum’s foul on Trey Burke in the closing seconds of Saturday’s win at MSG:

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Tatum commits the cardinal sin of not only fouling a jump shooter, but in an end-game situation that put Burke at the line to tie. Most coaches are loathe to chance fouling a three-point shooter. But there is no chance Stevens or any of the Celtics coaches would have Tatum play that potential game-tying attempt any differently, as they see the small risk of a foul being called more than offset by the better contest of the shot.

By teaching their players this technique of waiting for the motion to start and then to jump at shooters, Boston has mined gold from a coaching inefficiency. You can find hundreds of clips that some veteran coaches would shake their head at. One longtime college and NBA assistant coach told CelticsBlog, “It goes against everything I’ve ever taught my players. You just don’t leave your feet to contest threes. But I’ll be damned if this doesn’t have me questioning everything I’ve ever taught my guys.”

Stevens and staff introduced one more wrinkle in the last couple of years: contest the shot by jumping at the shooter and then leak out to the other end as soon as you know your team has the rebound. Watch Tatum here:

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Tatum contests and then he’s gone when he knows the Celtics have the rebound. This catches Boston sometimes, as they don’t always corral the miss. When they give up the offensive rebound, it generally leads to a wide open shot because the Celtics are down a man. One other challenge with this approach crops up when opposing bigs live around the arc. By doing the “run and jump” defense, it takes a big way out of position for rebounding. Fans have derided the Celtics’ rebounding woes, but it’s a trade-off that Boston seems more than happy to live with.

If you comb through the stats enough, you’ll see that opposing three-point percentage is all over the place. Except in Boston. The Celtics found something that worked and milked it for all it was worth. Then they doubled down.

The NBA is a copycat league. Coaches admit to stealing from each other all the time. Defending three-pointers seems to be the exception, at least for now. As the three-point shot continues to take on an even greater importance (teams are averaging 31.6 three-point attempts per contest entering Wednesday’s games), defending them also becomes that much more important. With long, bouncy athletes to challenge shooters, Stevens is getting better results than he ever has and it shows no signs of slowing down anytime soon.