How to Judge a Good Defensive Team from a Bad One in the NBA

The Portland Trail Blazers are not known for their defense, at least not in the Damian Lillard, CJ McCollum era. Is there any hope that will change? First we have to define what good and bad defense are. One Blazer’s Edge reader wants to know how to do just that, the subject of today’s Blazer’s Edge Mailbag.

Dave,

Everybody says we’re pretty bad at defense but how do you know? Some nights my eyes tell me that but sometimes I think they’re better than people say. They always use different stats and I want to know which ones really tell you how good they are?

Bobbie

Measuring defense is difficult. Every time someone says they have the answer, they don’t. Here’s a general rule of thumb: Are you winning as much as you should? Then your defense is probably adequate. If not, it needs work.

That sounds trite and cavalier, but honestly it’s not THAT much worse than people looking at defensive efficiency in isolation and saying, “This team has the 28th-worst defense in the league!” I don’t even know what that means. What kind of defense? Where on the court? Where do they succeed and fail? Are they sacrificing certain metrics for pace or shooting?

I like a slightly more holistic approach when it comes to defensive stats. I also want to give you a chance to make your own judgments, or at least make a more informed guess, as a lay person. I think both are possible.

Looking at six factors, all fairly easy to find, will give you a more nuanced look at your team’s defensive prowess than any “cocktail-mixed” single stat will do. This isn’t a magic answer, but it’ll render a decent idea of how the team is doing, where they’re excelling, and what they’re sacrificing.

Three-Point Percentage Allowed

Once upon a time, this was my second or third measure of defense. Now I look it up first every time, for the simple reason that all good teams want the three. That means all good defensive teams want to prevent easy shots from the arc. Giving up a high percentage usually means that your defense is falling apart at a basic level.

Overall Field Goal Percentage Allowed

This used to be the gold standard stat, the thing that made the San Antonio Spurs better than anybody else in the league no matter what else they did. The goal of the game is to score more than the opponent. Keeping a higher percentage of the opponent’s shots out of the bucket means you’re doing that.

This has been modified over the last 6-7 years by three-point shooting. Distance shots will hit at a lower percentage automatically. They yield 50% more points, though, more than justifying that lower success rate under most circumstances.

Looking at field goal percentage allowed and three-point percentage allowed side-by-side should give you a thumbnail sketch of how your team is doing.

You can fill in corners and details of that sketch with the following four stats.

Opponent Fast Break Points

Fast break points scored and allowed are biased by pace. Faster teams will generally register higher numbers each way than slower, ball-control teams. But even the best teams will wither if the opponent scores tons of easy buckets on the break.

The best way to figure out your team’s fast-break vulnerability is to see where they rank in pace (fastest, middle of the league, slow), then compare that to fast break points allowed (high, middle, low). If they match up, your team is fine. If pace is higher and fast break points allowed is lower, they’re doing well.

If you want to get really fancy, see how many points your team scores in transition itself, and whether their fast break margin is positive or negative. That’ll give you an idea whether it might be profitable for your team to slow down and play more controlled defense by sacrificing some overall speed, even on offense.

Slower-paced teams allowing a lot of fast break points and/or a negative transition margin are signs of trouble. If your team isn’t experiencing either, you may have to take the bad with the good on the break. Asking your team to limit the opponent’s fast-break points may also cost your team the opportunity to score fast themselves.

Opponent Points in the Paint

This is also a pace-oriented stat. Teams that generate more possessions per game will do the same for the opponent, which means more points scored and allowed. You’ll want to know where your team ranks in pace before judging how good or bad they are at paint defense.

Points in the paint allowed is a fairly tolerant stat. As long as your team ranks somewhere in the middle of the league, they’re fine. You want to pay attention if they’re Top 7 or Bottom 7 (or thereabouts). That doesn’t automatically indicate they’re a good or bad defense. It indicates you should check a little further.

Cross-reference points in the paint with three-point percentage allowed. If your team excels in both, they’re golden. If they languish in both areas, they’re in for a long season. If they split, you know they’re making compromises. Then you can begin to look for incremental changes they might make to up the bad category. Do they need more athleticism at the wing positions or size inside? You can run the permutations yourself. Just be aware that it’s hard to fine-tune a defense to excel at both. You’re not going to be able to do it with four good defenders and one non-defender. Your lineup and scheme both need to be solid or you’re always going to be choosing which areas of the court to favor.

Defensive Rebounding Percentage

The rebound is the ultimate end of good defense. Defensive rebounding percentage tells you how many of the available rebounds your team was able to gobble up, by percentage.

Beware that this is mostly a junk stat. The vast majority of the league falls within the same 3-4 percentage point band. As with points in the paint allowed, check to see if your team is at the very top or very bottom of the league, plus how far off the midpoint and how far below league leaders they are. If the difference isn’t much, ignore this stat entirely. If the distance between your team and the rest of the league is huge, they either have a nice incremental advantage or a potential problem.

Opponent Free Throws Attempted per Game

This is a hidden defensive stat, but it can become important in a couple scenarios. If your team has a natural gap in free throws allowed with the opponent for the night, they’re probably ceding a few points on average before the game even starts. In a league with tight average margins of victory, that matters. Second, if your team is going up against an opponent that excels in drawing fouls, that could be a nightmare.

Free throws allowed is pace-dependent, so see the caveats above. Even so, you’re going to see decent correlation between the best and worst defenses in the league and this stat.

Why Not Other Stats?

The flashier defensive stats—blocked shots, steals, forced turnovers—are missing from this list. Any aspect of the game can be indicative depending on the situation, but blocks and turnovers don’t tend to hold up well in the long run.

Steals and TO’s forced often have to do with pace. Faster teams tend to force and commit more turnovers. That may help them during the regular season, but when you slow them down in the playoffs, their defense looks completely different (usually not nearly as impressive). Since slowing down an opponent is as easy as walking and taking care of the ball, high forced-turnover rates end up being fool’s gold, or at best a nice addition to good defense rather than a sign of good defense themselves.

A certain amount of shot-blocking is desirable. If opponents don’t think twice before driving down your lane, they’re going to score easily. But shot-blocking is often a sign that the defense has already broken down. With most blocks, an opponent is near the hoop and free enough to attempt a close look. It’s great that your team blocked it, but since the best teams only swat away 7% of opponent shots, the other 93% are going to get attempted.

If your team is generating huge numbers of blocked shots per game, that means your 7% figure is big. It might also mean the 93% number is big. That’s actually bad. As with turnovers, blocked shots can be a nice candle on the defensive cake, but they’re not the foundation.

This is the same reason I prefer opponent points in the paint to opponent field goal percentage allowed in the paint as a defensive metric. By definition, the latter number is going to be high. Some teams can lower it, maybe even significantly, but that’s still an incremental improvement to a potentially bad problem. The best paint defense comes by preventing opponents from shooting in the paint to begin with rather than trying to compensate when they’re already there. Points in the paint allowed will give you a pretty good idea of how well your team is doing that, compared with pace.

I hope that helps! If you’re wondering about the Blazers, here’s how they rank in the six categories above (plus pace, for reference):

Three-Point Percentage Allowed— 15th (36.4%)

Overall Field Goal Percentage Allowed— 23rd (46.9%)

Pace— 7th

Opponent Fast Break Points— 28th (15.5)

Opponent Points in the Paint— 15th (46.4)

Defensive Rebounding Percentage— 14th (77.9%)

Opponent Free Throws Attempted per Game— 25th (24.6)

As you can see, they’re a pretty fast-paced team. That means you can adjust the rankings in Fast Break Points, Paint Points, and Free Throws Allowed to the good. That can’t mask that they’re giving up too many easy points at the free throw line and on the run. Those are huge, perhaps preventable, leaks in the overall defensive effort.

Portland’s overall field goal percentage allowed is nothing to write home about, but they’re much closer to the middle of the league in distance than the bottom. They’re barely below the 16th-ranked Phoenix Suns, who allow 46.2% from the field. They’re also in the middle in three-point percentage allowed.

If they can overcome their addiction to giving up easy points, the Blazers might actually become a middling defensive team. As it is, they’re probably bad, but calling them the worst in the league might be a stretch...or at least they’re not irredeemably so. On a given night they can look awful, but on balance, they’re not that bad.