Which Defensive Stats Matter Most in the NBA in 2021?

The Milwaukee Bucks have built a 27-14 record on three defensive pillars.

One, don’t let the other team get good looks. The Bucks are ninth in opponents’ eFG% despite being 20th in opponents’ 3PT%. They’re forcing opponents into bad two-point shots and stand fourth in that metric. Even though teams shoot well and often from three, it’s offset by their inability to get to the rim and get an easy two.

Two, limit the other team to one shot. Milwaukee is tied with the Orlando Magic for the best defensive rebounding percentage in the league.

And three, defend without fouling; nobody gives up a lower number of free throws per FGA than do the Bucks.

All of these stats, taken together, explain why they’re winning two-thirds of their games and why they’re still two games behind their expected W-L% according to Basketball Reference, which ranks them behind only the Utah Jazz on that front. Their plus-6.8 Net Rating speaks for itself; only Utah’s plus-7.9 is better.

But are these stats themselves predictive of winning? Let’s take a look at the top teams in certain stats and see if any of them are “the top teams are winning and the bottom teams are losing.”

We’ll start with the first one—opponents’ eFG%.

The top five teams in that stat are the Knicks, Jazz, Warriors, 76ers, and Lakers. That’s both 1-seeds if the playoffs started today, March 22, plus a 3 seed. Only the Knicks—more on them later—stand below .500 at 21-22.

Furthermore, of the top 17 teams in the NBA in opponents’ eFG%, you have to get down to 10th before you find another team with a losing record (the 19-22 Pacers), 13 of the top 17 teams have records at or above .500, and only the Oklahoma City Thunder (18-24, 12th) can genuinely be considered a truly bad team.

Of course, the Thunder can’t shoot for beans themselves, which explains as well as anything why they have a losing record despite a decent defense.

Then again, the Knicks shoot even worse than the Thunder do, but that’s the difference between first and 12th on a defensive stat and why the Knicks are 21-22. The Knicks’ shooting on offense is so awful that they become the exception that proves the rule.

At the opposite end of the scale, the other 13 teams include just two teams (the Nuggets and Trail Blazers, each 25-17) with winning records. The Nuggets accomplish this by having the fifth-best True Shooting in the league; the Blazers accomplish this…frankly, mainly through dumb luck. They’re a bad team with a good record, and not for nothing are they fully five games above the win expectation their Net Rating says they should have.

On paper, the Blazers should be 20-22. They just have an astounding eight wins by three points or less.

OK, so that’s that, right? Shoot the ball better than your opponent, or if you can’t shoot, play such tenacious defense that you win reasonably often based on your defense—see the Knicks.

Well, let’s do a bit more science here before we crown eFG% the One Stat to Rule Them All.

For one thing, that whole “keep your enemy off the offensive glass” thing.

It should surprise almost none of you that with offensive rebounding a lost art in the NBA, of the top 12 teams in defensive rebound percentage, just six have winning records, making this a crapshoot.

And other than the Bucks, the best teams are clustered around the 10 spot—the 2 seed in the West Phoenix Suns are ninth, and the Jazz and Sixers are 10th and 11th.

Now granted, you do want to secure the rebound and not concede a bunch of extra chances to your enemy—of the bottom 11 teams, eight have losing records, one is the aforementioned Blazers, and the other two are 22-21 (Warriors) and 22-20 (Hawks), not exactly playoff heavyweights.

But for the most part, if you’re around or maybe a bit better than league average on this stat, it’s more than enough to carry the day for you. Not exactly a stake-your-franchise-on-it strategy.

Now to that last—defend without fouling.

Free throws are free points, especially at the NBA level where teams make 77.8 percent of them. Maybe in college you can foul more and get away with it—the utterly unwatchable last two minutes of any close college game stands testament to that—but you can’t in the pros. (No, I’m not watching March Madness. College basketball sucks.)

But getting back to my point, there’s another solid but not spectacular correlation here. Divide the NBA at the median line and of the top 15 teams, 10 have winning records. Of the bottom 15, only four do, and—say it with me—one of those four teams is the wildly overachieving Trail Blazers.

While I’m on the subject, you want to know something that turns conventional wisdom on its head? The fourth of Dean Oliver‘s Four Factors—turnover percentage—seems to have an inverse correlation with winning.

That is to say, these days only bad teams go for steals, and the teams with the highest turnover percentage are all lousy.

Again, at the dividing line, just five teams out of the 14 currently on the plus side of even are in the top half of turnover percentage. The other nine—including the 1 and 2 teams in the West and the 2 and 3 teams in the East—simply do not force a bunch of giveaways out of their opponents.

And the West 3-seed Lakers and East 1-seed Sixers are just 12th and 10th in turnover percentage. Above them lie the dregs of the league, suggesting that teams that play a turnover-focused defensive style are doing so at the expense of sound, winning basketball.

Back in the 1990s and 2000s, steals were lauded as great defense, but in the 2020s, the opposite is true. Staying home defensively, focusing on directing the ball where it’s most likely to lead to a bad shot, then being at least a league-average rebounding squad, beats steals every day and twice on Sunday.

But to answer the question posed at the top of the article, sometimes basketball is just as simple as common sense would indicate.

Don’t let your opponents make their shots. Doesn’t matter if, like Milwaukee, you accomplish this by not letting the other team have anything inside the arc, or if like the Jazz, you simply do not allow the enemy to shoot from the perimeter and instead give up just a .338 3PAR and seventh-in-the-league 35.8 percent accuracy.