The Boston Celtics have jumped out to the best record in the league, and most of the credit goes to their incredible defensive start.
Last week I wrote about Cleveland’s struggles in just about every facet of defense to start the season. They’ve been so poor that it has left some hope for the rest of the Eastern Conference to finally overthrow LeBron James. The primary challenger thus far has been the Boston Celtics, mainly because they are the defensive juggernaut that Cleveland wishes to be.
Last season the Celtics were a solid defensive team. Not amazing by any stretch, but good enough when they had to be. They finished with the 13th best defensive rating at 108.4, but limited offenses to the fifth lowest eFG% in the league (50.3%).
They showed signs of becoming a championship-level defense, but they were too inconsistent to really put fear into the Cavs. They felt they were a couple of changes away from truly competing and this offseason they made plenty, but most didn’t foretell a huge defensive leap.
The Celtics traded away two of their best defenders in Jae Crowder and Avery Bradley, but they sent also their worst in Isaiah Thomas. Thomas was amazing last season and should be commended for developing into one of the best point guards in the league; but while he was dominant offensively, he was a defensive liability.
The Celtics replaced Thomas with Kyrie Irving who, while not known for his defensive prowess, isn’t as much of a mismatch as the diminutive Thomas often is. The additions of Aaron Baynes and Marcus Morris, as well as rookies Jayson Tatum, Daniel Theis, and Semi Ojeleye, finished an offseason that dramatically increased Boston’s defensive depth and versatility.
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Though the Celtics were hit hard by Gordon Hayward’s opening night injury, they have recovered masterfully to become that championship-level team led by their defense, featuring a league-best 97.8 DRtg, the fewest points allowed per game in the league, and an Opponents’ eFG% of 48%.
While the Celtics are littered with great individual defenders like Marcus Smart and Jaylen Brown, their key has been the aforementioned depth. Right now, each of the Celtics’ top eight players have a DRtg under 100. That stat is pretty remarkable on its own, but when you realize that only 27 players in the entire league have played 100+ minutes and also have a DRtg under 100, the fact that the Celtics have nearly a third of them becomes incredible.
If you were trying to find a hole in the Celtic defense you would likely look inside given their primary centers in Al Horford, Baynes, and Theis are all undersized. But so far, they’ve been pretty strong in the paint. While they allow a league-average 61% shooting from inside six feet and don’t block many shots, they give up only the fourth fewest points in the paint per game.
The other risk in running with a smaller frontcourt is allowing offensive rebounds, but the Celtics have done a great job limiting second chances. While Horford is their leading rebounder at only 8.8 per game, Boston has used a very effective gang rebounding approach. They have eight guys averaging at least 4.5 rebounds per game and as a team grab an exceptional 81.2% of available defensive rebounds.
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The fact that there isn’t a glaring hole in Boston’s defense is really their greatest strength. They are one of the most versatile defenses in the entire league.
Outside of the point guards, almost every Celtic is between 6’6” and 6’10”. They almost always run with three wings on the floor which gives them lots of length and quickness along the perimeter. They do an exceptional job getting in passing lanes and covering for each other, leading to the fifth-most deflections, fifth-most steals, and second-most shot contests in the league.
Possibly the greatest benefit to this versatility, though, is the ability to defend against screen-heavy offenses. In the play below, Boston’s versatility allows their center, power forward, and shooting guard to all switch on screens without a creating huge mismatch.
Knowing you are likely to switch on screens also takes a lot of the guesswork out of an NBA defense. For a roster so full of first and second-year players, this is a huge blessing. Tatum, Ojeleye, Theis, Jaylen Brown, and others have pretty seamlessly transitioned into a top-tier NBA defense.
Out of all the Celtics, however, Irving probably benefits the most from switching. Irving is not a defensive stopper, but he is athletic enough to stay in front of his man in one-on-one scenarios. His biggest defensive shortcoming, however, is that he dies on almost every screen set on him. I’ve picked out just one example of this, but something similar happens nearly every time he is asked to fight through a screen.
He just kind of stops, and in Cleveland this became a huge problem. Offenses would attack Irving with pick-and-rolls over and over again, very often resulting in open shots. The Celtics do a very good job of minimizing this problem by switching those screens and in this case, Horford gets out in time to contest the shot.
While switching is a very useful tool, it isn’t a guaranteed fix. Sometimes it creates such a big mismatch that it just isn’t viable. You can live with Kyrie switching onto Jarrett Allen in the play above, but you’d be much more worried about him guarding a better offensive player like Kristaps Porzingis or Joel Embiid.
When that is the case, Boston’s bigs do a great job at flashing out to stop the ball handler and then recovering back to their man to prevent a mismatch. This play is just a few seconds after the previous one, but this time Horford flashes up allowing Smart to recover onto his man, then falls back and eventually forces a turnover.
Having the athletic bigs like Horford and Morris is a huge advantage in that scenario. While they sometimes struggle to get back to the roller, they do an exceptional job in limiting the P&R ball-handler to just 0.73 points per possession. Being able to consistently take away such a staple for most offenses gives Boston’s defense a huge advantage.
While it is still early, the Celtics have been very impressive to start the year. As expected, their offense has struggled to recover from Hayward’s injury, but their defense has more than held up its end of the bargain. Fifteen games isn’t the largest sample size, but we have seen enough to know that this Celtic defense isn’t going away, and that makes them a viable threat for the Eastern Conference crown.
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