The Spurs currently rank third in the league in defensive efficiency, allowing only 95.7 points per 100 possessions. Considering the best defense last season allowed 96.7 points per 100 possessions, the mark seems unsustainable. But it's undeniable that the Spurs have been fantastic on that side of the ball. Their success in that area is even more impressive considering they have not been able to count on defensive linchpin Tiago Splitter so far this season and the players getting his minutes are not even close to his level on that end. So how are they doing it?
The first thing to establish is whether the Spurs have simply padded their numbers by playing against bad offenses. If your opponent typically has a hard time scoring, holding them to their poor average should be enough to have a sterling defensive rating. So I looked at the average offensive rating the Spurs' opponents have had (excluding the game against San Antonio, of course) and compared it to their offensive rating in their game against the Spurs. Here are the results:
The Spurs have held every opponent below their average offensive rating, sometimes by a large margin. The only opponent who even came close to eclipsing their season average was the Mavs on the first game of the season. Even in their losses, the Spurs' defense has given them a chance. They've had their issues scoring, but defensively they have been great.
So the numbers are meaningful, or as meaningful as they can be considering the season is young. With that established, let's see exactly how the Spurs are doing it.
The Spurs miss Tiago's rim protection
The first thing I looked for were the rim protection numbers. Their ability to seal off the paint was a key component to the Spurs' defensive success last season and while it was possible that San Antonio was doing just fine in that area without Splitter, that's not the case.
The Spurs are allowing one more shot at the rim per game than last season (26.1 in 2013/14, 27.1 in 2014/15) and opponents are converting at a 1.5% better rate (58.6% in 2013/14, 60.1% in 2014/15). In contested field goals at the rim opponents are shooting 54% while last season that number was 50.7%. The Spurs interior defense hasn't been as good so far and it's not hard to see why.
Aron Baynes is allowing opponents to shoot a gargantuan 62.5% at the rim in shots he contests, one of the worst marks in the league. For reference, he ranks between Kevin Love (63.6%) and Luis Scola (62.2%) among players who are on the court at least ten minutes a game and contest at least three shots a game at the rim. Jeff Ayres has been markedly better (50% allowed at the rim) but he hasn't played enough for his numbers to make an impact.
Tim Duncan has been amazing (only 45% allowed at the rim on a huge number of attempts) and has kept the rim protection issues from being a devastating blow to team defense. But the Spurs are clearly not protecting the rim well. They are however, doing other things that are having a big impact.
The three-point defense has been stellar
The Spurs are only allowing opponents to shoot a meager 27.5% from beyond the three-point line, the lowest percentage in the league. Teams are shooting only 30.9% from the corner. For reference, the second best defense in the league, the Warriors', is allowing 47.2% in about the same number of attempts. And in above the break (non-corner) threes, the Spurs 26.8% is the second lowest mark in the league, with only the Warriors' being better.
Normally I wouldn't put too much stock in corner three defense because those shots are usually open. The Spurs could have simply been lucky that their opponents were missing. And there's obviously some of that going on. But going over the video it's clear the Spurs are being very smart in the way they defend. Most of the corner looks come from opponent small forwards that are not elite shooters. Kawhi Leonard basically leaves them open to help and then recovers fantastically thanks to his ability to cover ground. Cory Joseph is also great at closing out. The egregious mistakes that result in open looks for good shooters often come from Manu Ginobili and to a lesser degree Danny Green overhelping and Marco Belinelli not being fast enough to close out. But overall a surprising amount of opponent corner threes have been contested.
That being said, those numbers are clearly not sustainable. The team that allowed the lowest three point percentage last season allowed 33.2%. And the lowest mark allowed on corner three-pointers was 34.9%. Teams will eventually start hitting more shots. But the fact that they haven't so far has been a boon for the defense.
Defensive rebounding and avoiding fouls: two Spurs staples
The Spurs are leading the league in defensive rebound percentage with a ridiculous 80.9%. That means they rebound their opponent's miss in four out of five opportunities. That's another mark that is unsustainable but San Antonio has traditionally been near the top in defensive rebounding as a team.
Fortunately for the Spurs, they don't miss Splitter in this area. Aron Baynes and Jeff Ayres are very good rebounders and Tim Duncan is still an elite defensive rebounder. His 29.9% ranks him fifth in the league among players who qualify for the leader board. But it's not just the centers doing work. Kawhi Leonard is rebounding like a big man and Cory Joseph is putting up very good defensive rebounding numbers for a point guard.
Another staple of the Spurs' defense across the years has been their aversion to fouling and that has carried over to this season. Even though the backup bigs - especially Ayres and Baynes - are fouling like crazy, the rest of the team has remained as disciplined as ever, allowing the Spurs to concede the fifth lowest amount of free throws per game.
As a result of their excellence on the defensive board, the Spurs are not allowing a lot of second chances. And since they are not allowing a high percentage from three or a lot of free throws, they are able to contain even very potent offenses.
Can the Spurs remain elite on defense?
Even though the numbers are clearly unsustainable, the process that has led to them is sound. So the Spurs should remain among the league leaders in those categories. The defense will surely suffer a bit when Marco Belinelli and eventually Patty Mills return and take minutes away from Joseph and Leonard or Green. But Tiago Splitter's return will likely have an stabilizing effect on the interior defense, which should offset the drop off on the perimeter D.
Unless injuries strike or something strange happens, expect the Spurs to remain among the elite on defense.