The Definitive Guide to Gobert’s DPOY-Level Impact

Rudy Gobert is impacting the game defensively at a historic level. (Alex Goodlett)

Two drastically different defenders have emerged as frontrunners for this year’s Defensive Player of the Year award. Ben Simmons is an elite, versatile defender who locks down opposing teams’ best players. The other, Rudy Gobert, is a juggernaut defensive anchor who’s so dominant that his team’s defensive scheme funnels opposing players towards him.

While their body types are not actually that different (Gobert is 7′1″, 245 lbs., Simmons 6′11″ and 240), the contrasting-styles issue is a legitimate hurdle to determining who is the league’s top defender, but it shouldn’t end of the inquiry. The Defensive Player of the Year should be the best “defender” in the truest meaning of the word. If the purpose of defense is to stop the other team from scoring, the DPOY should be the most effective at accomplishing that goal, regardless of play style.

There are two overarching ways to determine this: the eye test and the stats test.

Why Stats Matter to the DPOY Race

The first is the eye test, which is simply judging talent by watching. But there are several issues with this test. On the surface, eye-test knowledge is the easiest to obtain, but it might be the hardest to communicate. Even the casual fan sees why a player like Simmons is valuable; however, persuading someone that Simmons is a better wing-defender than Jrue Holiday, Kawhi Leonard, or Giannis Antetokounmpo isn’t easily provable without some empirical proof.

On a deeper level, eye-test knowledge requires a trained eye and lots of time. This is precisely why Jazz fans struggle to communicate the defensive value of Gobert to casual fans who see him play a couple times each year. And unless you know what to look for, Gobert can look more like Bismack Biyombo than Dikembe Mutombo.

The most powerful eye-test bias is simply own our subjective lens through which we see the game. I hate to break this to you, but referees don’t just make bad calls against your team, Sixers fans don’t all just magically fall into believing only Simmons deserves DPOY, and your favorite players can’t all be the greatest of all time. Fandom, popularity, and likeability all play into the fact that the mind sees what it wants to see.

Factoring in all of these variables, simply watching basketball doesn’t always lead to an accurate understanding of a player. I’m frankly stunned that an unappealing, oft-hated foreign player on the Utah Jazz with a nebulous and nuanced defensive impact has any notoriety outside the state of Utah. This is why the second way of assessing defensive value is so helpful: stats.

Of course, there are some weaknesses with defensive stats as well. For one, some stats favor one player-type over another. However, statistical biases are not like those involved in the eye-test; they’re not based on random scales of fandom, popularity, or likeability. Stats track what you want them to track. So, if you understand which way the numbers tend to lean, you can correct for that bias. For example, if an advanced stat like D-RAPTOR is more favorable to centers, you can give some wiggle room to guards and forwards or compare them instead to their peer group. Another issue with some stats is they can take real effort to understand. I’m sure you’ve seen FiveThirtyEight’s RAPTOR or Bball-Index’s LEBRON, but what are they even measuring?

In this article I’ll do my best to demystify some key statistical categories in order to analyze the Simmons vs. Gobert debate:

• Box score & tracking
• Defensive shooting
• On/Off impact
• Varous advanced metrics.

By the end of this article, you should have plenty of fodder for Twitter discussions with people who think Simmons is a “lock” for DPOY.

Box Score & Tracking

From NBA.com

Box Score: The traditional box score is the low-hanging fruit of the stat world, but it still tells us something. I’ll spare you the more obvious definitions, but remember that a block can also reflect a future paint deterrent, a steal can provide a chance for fast-break points, and a rebound can either reflect a stat-stuffing grab or a player sealing a win. I’ve also added a couple of non-traditional box score stats via the NBA’s tracking cameras. A “shot contested” is when a player closes out and raises a hand to contest a shot prior to its release. The total number of shots contested can reflect the frequency of a player’s impact on another team’s shooting. A deflection is simply getting a hand on the ball on a non-shot attempt. Keep in mind that each of these stats skew towards certain play-styles and player-types: a guard might be more likely to get steals and deflections, while a big man might naturally block and contest more shots.

DPOY Impact: In the box score battle, Gobert outperforms Simmons in all big-man stats like blocks, rebounds, and shots contested, while Simmons wins in the wing-defender stats like steals and deflections. Comparing strengths, Gobert ranks #2 in blocks (would be 123rd all time) while Simmons ranks #6 in steals (outside top 250 all time). Gobert is also #2 for shots contested while Simmons is #3 in deflections. Over the 5 years that the NBA has tracked “shots contested,” only 5 other players have finished the season with 15.4 shots contested per game. In that same time, 11 players have finished with 3.6 deflections per game.

Winner: While it may seem like Gobert has a greater impact on these box score stats, some of that is based on role/position. This one is too close to call. TOSS-UP.

Matchup shooting

Via NBA tracking data

Matchup Shooting: Next, we move into a player’s effect on opponent shooting. The NBA uses tracking software and special cameras placed on the catwalks of NBA arenas to determine who is primarily defending a shot. DFG% tracks opponents’ shooting percentage against a certain defender, but doesn’t take into account differences in shooters or shot types. That is why the most important stat here is DIFF%, which subtracts DFG% from the opponent’s typical FG%, giving you a far more specific overall impact that a player has on opponent shooting. If a player has a negative DIFF%, they hold their opponents to a lower shooting percentage than the opponents’ average.

DPOY Impact: Simmons’ opponents shoot 0.6% worse than Gobert, which is nothing to ignore. But DFG% misses some context about the types of shooters and shots each one guards. According to Bball-index, Simmons has a higher Matchup Difficulty, which may imply that he’s guarding players with a higher overall FG%. On the other hand, Gobert often contests shots closer to the basket, where expected FG% is substantially higher. DIFF% addresses some of that noise, and Gobert forces players to shoot 7.2% below their average, which ranks #1 in the NBA. In fact, since 2013-14 when the NBA started tracking this stat, only eight players have finished with a higher DIFF%. Simmons forces players to shoot 5.1% below their average, good for 13th this year among players with at least 30 games and five contests per game.

Winner: Gobert runs away with this one.

On/Off Impact

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ON/OFF: On/off stats reflect how a team performs while a player is on the court vs. off. Defensive on/off stats show how his team performs defensively when he’s on court as opposed to sitting. Negative numbers here are best, as they mean the team gives up fewer points when a player is on the court. The other categories look at how the team performs at impacting opponents’ effective FG%, causing turnovers, and limiting offensive rebounds and free throws. These numbers are not calculated per game, but per 100 possessions. Keep in mind that on/off numbers can be skewed by a player’s supporting cast, and even by who their replacement is in the rotation.

DPOY Impact: Gobert basically outperforms the NBA field in three out of the five: points swing, eFG% swing, and FT swing. When Gobert is on the court vs. off, opposing teams score 11.9 fewer points, shoot 5.7 percentage points worse from the field, and go to the FT line 5.7 fewer times. Since on/off-points allowed (defensive rating swing) is the stat here most closely tied to overall defense, let’s compare Gobert’s -11.9 to some previous DPOYs.

From Cleaning the Glass

I looked up the defensive swing of every DPOY going back as far as the Cleaning the Glass database goes (2003-04). The chart shows that not a single DPOY in the last 18 seasons has beat Gobert’s -11.9 on this metric. That’s pretty stunning.

The Jazz cause fewer turnovers when Gobert is off the court. Simmons, on the other hand, is elite in his impact on the 76ers’ ability to limit offensive rebounds. He’s also solid in causing turnovers. But one strange piece to the puzzle is that the 76ers actually force teams to shoot a lower eFG% when Simmons is on the bench.

Let’s try to poke some holes in Gobert’s numbers. Perhaps the Jazz as a team are actually not very good in Gobert’s three dominant categories, and since Gobert’s the only one that is, this unjustly inflates his impact numbers. Looking to FT Rate, Gobert’s primary backup (Derrick Favors) does have a high foul rate, so that might explain some of Gobert’s impact on FT Rate. But the Favors piece cuts both ways, since he’s also a solid defender, who the Jazz picked back up to fix their bench issues. As a team, the Jazz allow the #2 fewest points (107.8), the #1 lowest eFG% (50.7%), and the #2 lowest FT rate in the NBA. Gobert averages 31 minutes out of the full 48. That’s 17 minutes left open. If Gobert’s teammates are so bad in these categories, how does the team still lead the league in overall defense?

Similar context might help explain some of Simmons’ on/off numbers. He plays next to Seth Curry, and when they sit down, two amazing defenders in Dwight Howard (3x DPOY) and Matisse Thybulle replace them. But it’s also fair to say that Simmons often plays next to Joel Embiid, who happens to be another DPOY candidate this year and Danny Green, another solid defender.

Winner: Overall, there’s no real way around it: Gobert’s numbers outpace Simmons here.

Advanced Stats

Various advanced metrics favor Gobert.

Advanced Stats: These metrics are generally called “catch-alls” because they represent various attempts to summarize all of a player’s defensive contributions. I’ll do my best to simplify the description of each of these as they can get very complicated. I also want to note that while we tend to give less credence to the metrics we don’t understand, the research process actually led me to believe that these catch-alls are all carefully and thoughtfully crafted. The more I researched, the more I believe that the RAPTORs and LEBRONs of the world are actually more accurate than anything we’ve covered so far. Still, these metrics tend to like big-men, so we’ll also compare Simmons’ numbers to other, similar players.

This is based on Basketball-Reference’s version of DRtg, which is a little different from the NBA.com version.

D-Rating: Defensive rating estimates how many points the player allowed (per 100 possessions) while on the court. According to basketball-reference.com, the “core” of this metric is the defensive “Stop.” “Stops take into account the instances of a player ending an opposing possession that are tracked in the box-score (blocks, steals, and defensive rebounds), in addition to an estimate for the number of forced turnovers and forced misses by the player which aren’t captured by steals and blocks.” Simply put, D-Rating is a simple but powerful tool that reflects how well other teams perform on offense when one player is on the court playing defense. Of course, this can be skewed by the player’s supporting cast, so that’s something to keep an eye on.

DPOY Impact: Gobert runs away with D-Rating fairly easily, but to make sure we aren’t misreading the numbers, let’s look at how much their teammates’ defensive abilities might impact the rating. For the sake of simplicity, let’s just take the individual career defensive ratings of the eight most common players to play next to each. While career ratings won’t give you a perfect or current understanding of these players, they’ll give you an idea of how good these players have been across their career. The following table is sorted by players who have played the most minutes next to Gobert/Simmons to fewest minutes.

Source: B-Ref

Gobert’s most frequent on-court teammates include Conley (108), Mitchell (108), Bogdanovic (112), and O’Neale (107). The average of those four fellow starters — 108.7 — is significantly worse than Gobert’s 2020-21 rating, not even considering the league-wide offensive explosion this year. Simmons’ peers in the 76ers’ starting lineup (Green, Curry, Harris and Embiid) have an average career D-rating right in the ballpark of Simmons’ current DRtg. Comparing the teammate averages, the fact that Simmons’ teammates that much better than Gobert’s goes to shows the impact Gobert is having leading a core of average defenders to the league’s top defense, while Simmons is surrounded by plus defenders.

Winner: Gobert.

D-WS: Defensive Win Shares measure a player’s defensive value in terms of wins, and are primarily based on a player’s defensive rating. In much more technical terms, according to basketball-reference.com, D-WS uses defensive rating to quantify a player’s “marginal defense” (player’s defensive impact on team success). Marginal Defense = (player min. played/team min. played) * (team defensive possessions) * (1.08 * (NBA pts per poss.) – ((NBA Average Def. Rating) / 100). You then divide marginal defense by the NBA marginal points per win to get D-WS. Marginal Points Per Win = (NBA points per game) * (team pace) / (NBA pace). Keep in mind that win shares values playing time, unless you’re looking at Win shares per 48.

DPOY Impact: As with DRtg, Gobert comes out on top as he leads the league in Defensive Win Shares. Still, Simmons is not so far off at 8th.

Winner: Gobert

From B-Ref

D-BPM: Box Plus/Minus estimates how much a player helps his team when he’s on the floor by looking at the traditional box score (no play-by-play data or non-traditional stats). According to Basketball-Reference, D-BPM looks to a player’s box score (rebs, stls, blks, pts allowed, fouls), position (PG, SG, SF, PF, C), and team performance. BPM also uses a regression, which is a statistical method that helps identify the relationship between variables to determine the relative impact of each box-score variable on the team performance. So, if a steal is more impactful than a rebound, this will account for that. +0.0 is the NBA avg. and +2.0 means the team is 2 points better with that player on the floor compared to an average player (per 100 possessions). The 5 best single-season D-BPM scores of all time range between McMillan’s +5.53 (#1) and Eaton’s +4.29 (#5). No player beyond 1994 breaks into the top 5. Finally, like all stats, D-BPM has some shortcomings. Since traditional box scores contain very few variables tracking defensive impact, D-BPM is not the most reliable stat in the world.

DPOY Impact: Gobert and Simmons are close, though Gobert still has the higher number. Gobert’s current D-BPM would rank #199 in the best single-season D-BPM, which is actually nothing to write home about, but Simmons’ 1.8 fails to crack the top 250. Ironically, Simmons’ 2017-18 season would rank #205 all-time.

Winner: Gobert.

DPS: Defensive Points Saved is one part of NBA Math’s TPA (total points added), which uses D-BPM as a starting point. However, DPS implements a few subtle differences, including weighing how many possessions the player actually plays. The actual calculation is described here. Over the last 10 seasons, the 3 best DPS scores include: (#1) Joakim Noah in 2014 at 291.45, (#2) Andre Drummond in 2018 at 278.83, and (#3) Rudy Gobert in 2019 at 274.63.

DPOY Impact: Gobert’s number here is nearly twice that of Simmons. Since DPS values the number of possessions played, Gobert’s number might be inflated compared to Simmons, primarily because Simmons has missed a few games this year.

Winner: Gobert.

From FiveThirtyEight

D-RAPTOR: RAPTOR (Robust Algorithm using Player Tracking & On/Off Ratings) is FiveThirtyEight’s NBA stat that goes beyond D-BPM. RAPTOR looks to two main variables: (1) box score stats (including player tracking, play-by-play data) and (2) on/off stats. D-RAPTOR, for example, looks at “how often the player was the nearest defender on an opponents’ shot,” “how often those shots went in,” and “how many points and rebounds were scored by opponents at the defender’s position.” RAPTOR also goes beyond the normal on/off stats by evaluating a bunch of lineup variations. Since 538 found that “on-court/off-court stats provide useful [but] quite noisy” measures of player value, they added more weight to the box score component. A much more antiquated explanation of the metric can be found here. Like BPM, RAPTOR measures player’s impact to his team’s performance (per 100 possessions) relative to a league avg. A player with a D-RAPTOR of +3.4 would improve his team’s defensive performance by 3.4 points per 100 possessions while he’s on the court.

DPOY Impact: According to D-RAPTOR, Rudy Gobert is having the greatest defensive season of all time. Considering that the average D-RAPTOR of all 38 previous DPOYs is 4.01, Gobert is almost double that mark. Simmons, on the other hand, is not close.

Source: 538

To be fair, D-RAPTOR could inflate numbers of NBA big-men and undervalue non-centers. That’s why we also compared Simmons’ current season to a few notable defensive wings and guards from NBA history. Simmons does not come close even to this perimeter-defending peers. MJ, Kawhi, T. Allen, Metta, all show up at the top, above +3.6. Only four of the past 11 non-centers to win DPOY fall below the +2.0 threshold (Rodman, Cooper, Moncrief x2), and this group’s average D-RAPTOR is 2.27.

Winner: Gobert.

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D-LEBRON: LEBRON (Luck-adjusted player Estimate using Box prior Regularized ON-off) is somewhat similar to RAPTOR, as it evaluates a player using box score and advanced on/off stats, but LEBRON also leans into the player’s role (or position) on luck-adjusted numbers to, as Bball-index says, “fetter out inconsistency.” Luck/variance adjusted numbers adjust a player’s on-off stats by controlling for factors out of their control. For example, D-LEBRON controls for opponent 3P%, which is often more closely tied to variables outside a player’s control. Much like other impact metrics, 0.0 is league average.

DPOY Impact: Just like D-RAPTOR, D-LEBRON says Gobert is having one of the greatest defensive seasons ever. Simmons is not close.

Winner: Gobert.

Historical context for Gobert’s incredit D-RAPTOR and D-LEBRON stats, from 538 and Bball-Index.

Putting it all together

Stats like D-RAPTOR, DRPM, D-LEBRON, DBPM, DWS, D-Rtg, DIFF% don’t capture everything. For one thing, they can be biased towards big men. There are subtle reasons for this, and they’re worth considering, but it’s also important to ask whether it’s a complete coincidence that NBA centers have a greater impact on the box score, on plus/minus, etc. Rim protectors do just that: they protect the rim, impacting more shots and plays than any other player due to where the team places them on the court. So, perhaps they are the more valuable position defensively, and perhaps the numbers aren’t unjustly inflated towards them, perhaps they’re just reflecting impact.

Considering that so many of these stats are geared towards measuring the goal of defense (to stop the other team from scoring), if someone other than Gobert were truly the NBA’s best defender this year, I believe there would be at least ONE defense category where he was ahead of Gobert. The numbers speak for themselves: Gobert is the most deserving of DPOY. Simmons’ ability to guard 5 different positions matters, but Gobert can simultaneously neutralize all 5 opposing players by anchoring an entire system designed around his historic strengths.

Here’s a graphic will all of the stat categories from this article.