Offense and defense ratings adjusted for position bias

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Introduction

A few weeks ago, I took a look at players’ offensive and defensive ratings accounting for team performance as a whole. After doing so, I noticed that players’ performance seemed to correlate greatly with their positions, particularly on defense. I didn’t give this much thought at the time, but started thinking about it more in depth over the weekend.

Here are the questions I asked: What if some defensive and offensive ratings are biased towards certain positions? It would make sense that a big tall guy standing near the rim is more impactful on defense than a small guy on the perimeter. But does that necessarily mean he’s a better defender, or just plays a more important defensive role? And, if the latter, how can we more effectively compare the defensive performance of two players at two different positions?

Preliminary analysis and measures of interest

I started by collecting the data of all players who have played at least 25 games and at least 22 minutes per game. Then I disaggregated the data by position. Here are the results:

PositionCountAverage DRtgAverage ORtgNet
C23102.35108.916.57
PF37104.30107.843.54
PG39106.90106.36-0.54
SF43106.12105.30-0.81
SG42107.71107.21-0.50

These results are hugely important. Just by virtue of their position, centers automatically look amazing compared to other players. This is true not only defensively, but also offensively (possibly due to offensive rebounding presence?). In fact, the average center has a net rating of 6.57. Power forwards also receive a bump in their stats due to their position/role. The other three positions are actually a net negative.

These results beg us to ask, if a center or a power forward has a good looking rating, is he actually good, or just playing a position that the stats bias positively?? Conversely, if a guard/wing has a bad looking rating, is he actually bad, or just playing a position that the stats bias negatively? And how the heck can we compare players across positions given these biases?

My solution is to create two stats, adjusted defensive rating and adjusted offensive rating. These two stats are calculated by subtracting a player’s individual rating by the average rating of the player’s position. I do this in order to eliminate the position bias inherent within these stats. In effect, it creates a measure similar to baseball’s WARP (wins above replacement player). Players’ performance are measured relative to an average player at their positions.

Technical information

The above chart shows all players’ adjusted defensive ratings on the x-axis and adjusted offensive ratings on the y-axis. Filters on the top left allow you to filter the chart by team and position. A tab on the upper left allows you to switch to a table view, where you can then sort all the players by their adjusted defensive and offensive ratings, and their adjusted net ratings (adjusted offense minus adjusted defense). Remember, for defense, negative numbers are better.

Limitations

All data is unweighted. Number of games and minutes played are not considered in players’ ratings or averages.

Observations

Oh man, where to even start. I guess let’s begin with some boring but important things. First, centers are the most valuable position. In particular, centers who do “centery” things have the most valuable roles. Just having them on the floor, even if they’re average at what they do, is a huge boon to team performance. The “stretch 5s” like Bargnani and Pau Gasol don’t pass the measurement test. That the Houston Rockets have had injured big men the whole season might be even more important than initially thought.

Second, the range of offensive performance (-20 to +20) is twice that of defensive performance (-12 to +8). So a player can be good or bad on defense, but can be REALLY GOOD or REALLY BAD on offense.  For example, a team receives a 20 point defensive bump per 100 possessions by upgrading from Andrea Bargnani to Roy Hibbert, but a 40 point offensive bump by upgrading from Jeff Taylor to Kevin Durant.

The best defender in the league is now Paul George. The best offensive player in the league is still Kevin Durant. Durant is also the best net player in the league. Durant also might be a golden god.

Here's the Houston Rockets

Here’s the Houston Rockets

Dwight Howard suddenly looks much less impressive now that his performance has been adjusted. He’s a little above average defensively (though still the best on the team) and is below average offensively. James Harden, on the other hand, is redeemed a bit. He’s one of two players who are above average defensively and offensively, with Terrence Jones being the other. And, no matter how one slices and dices the data, Patrick Beverley’s supposed defensive prowess still does not show up. I’m starting to think that the critics who claim that his defense is more showy than effective are correct. Unfortunately for the PG position, Jeremy Lin is just as bad.

In conclusion:

The Indian Pacers will crush you

The Indiana Pacers will crush your face into a hot mess

The Milwaukee Bucks will not

The Milwaukee Bucks will not

 

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Total comments: 19
  • thejohnnygold says 7 months ago

    It seems like a good pairing with this data would be looking at player line-ups and who they are spending the majority of time on the court with. It helps paint a fuller picture and contextualize the ratings.

    Here is Jeremy's 5-man splits from basketball-reference.com:

    Jj2vVO9.jpg

    And here is Patrick's (sorry for the bad cropping):

    Ao7Lp6k.jpg

    So, I've highlighted some of the stats that stood out to me--primarily turnovers and the fg differential (most of these stats represent a Net 100 result--so a -7.7 FGA number means we take 7.7 fewer shots than our opponent on a per100 basis on average.

    Lin's turnover numbers are significantly higher than Bev's looking at their top 4 lineups: 32.5 for Lin vs. 10.2 for Bev. That is HUGE. I realize they are not all his, but we are looking at team performance.

    I immediately looked at the net fga's and saw a pretty obvious correlation. Our opponents take way more shots than us because we are coughing it up without getting a shot off and giving them extra possessions in the process. Despite higher efg%'s and free throw attempts in most line ups we are struggling to outscore our opponents. Offensive rebounding is also a big culprit in this.

    Getting back to turnovers, I'm not blaming Lin entirely--those first two line ups with Howard, Harden, Parsons, and Lin are a statistical nightmare for turnover probabilities. The result is a net positive in points, but not by very much.

    It is plain to see the difference, and overall effect, Beverley has on the offense. Lin's top 4 opponents shoot a combined +77 fga's per 100. With Bev, that number drops to 55.8. That number almost perfectly reflects the turnover differential between the two we calculated earlier. Lin is +22.3 in turnovers and Lin is + 21.2 in fga's.

    These charts show a lot of info. and I invite people to look them over. You can also get better sample sizes by going to Lin's and Bev's splits pages which also offer 4, 3, and 2 man pairings (the minutes played are significantly higher)---mostly they reinforce what these already show. Again, I am not trying to vilify Lin--I am addressing the discrepancy in their offensive rankings from the original post.

    Once again, the data shows and supports our starting five. Of all the lineups with any significant playing time that one boasts excellent numbers. We make +1.5 more shots while taking 7.7 fewer, we are +5.9 in scoring margin, and we are only +1.1 in turnovers.

    There is no argument whether Lin is a more skilled offensive player than Beverley--when viewed in a singular context. The question is how does their play affect the team overall? Look at Bev's third lineup (which has Lin in it). That is one we use at times to end games. It is the only one with a turnover rate in our favor. The problem is our shooting and rebounding drop off a cliff and our net points are -17.2.

    At the end of games, only one of Lin/Beverley should be on the floor--as evidenced by the lineups above. I'm fine with either one as they are generally utilized to space the floor on spot up threes--not to dribble/pass. Bev is shooting 31% on threes in January while Lin is shooting 24% (both are shooting 33% for the season).

  • rocketrick says 7 months ago

    Very true. Look at Bev's +/- and he "is" clearly the best Rockets player by that measurement. And we knew that Bev is no more than 5th best player on the team. If you look at PER, Lin and AB are above Bev, so Bev is the worst among three PGs? Depend on which data you use, you will come to different conclusion.

    However, in my opinion the Rockets are a better team going forward with Beverley as the starter and Lin coming off the bench to give the necessary and most important energy. What will be interesting going forward is whether Beverley or Lin will be on the court in the final 5-7 minutes of the last few regular season games this season and beyond. Some think that Coach McHale favors one over the other, but I believe whoever contributes to the team effort overall more will be the one on the court in those last few minutes of key games. Go Rockets!!!!

  • Richards says 7 months ago

    I think these are two excellent points of conversation. As someone who obsesses over stats and data, arguably my number one rule is to never trust one piece of information too much. All data tell different stories. It's important to look at a great variety of information to better understand a situation, and also to have a grasp on what each piece of information communicates.

    Regarding offensive and defensive ratings, it is very much a team related stat. That's why, in a previous post, I looked at individual ratings relative to team ratings. In this post, I'm looking at individual ratings relative to other players of the same position. Again, two different pieces of information that flesh out different parts of the same situation.

    The four players I quoted above are good examples of why looking at lots of information is necessary. When we look at, say, Beverley and Lin play, we see two very different playing styles. Lin appears more offensively aggressive than Beverley. If my life depended on one of them driving to the basket, I'd choose Lin. Offensive rating, however, is not a measure of how good someone is at driving to the basket. It's points per possession. Considering Lin's higher turnover rate, usage rate, and who might be on the floor with him, it's understandable why possessions with Lin on the floor might result in fewer points on average than Beverley. It does not mean Beverley is a better offensive player; he's just playing a different game.

    The same can be said for Howard. If my life depended on either he or Robin Lopez posting someone up and making a jump hook, I'd choose Howard. But Howard also has a higher turnover rate, usage rate, and much lower free throw percentage, whereas Lopez plays with more knock down three point shooters. Howard is trying to initiate, while Lopez is just trying not to screw things up. All these considerations matter greatly when calculating points per possessions. Hence, Lopez is leading all centers in adjusted offensive rating whereas Howard is middling. It does not mean Lopez is a better (or the best) offensive center; he's just playing a different game.

    Very true. Look at Bev's +/- and he "is" clearly the best Rockets player by that measurement. And we knew that Bev is no more than 5th best player on the team. If you look at PER, Lin and AB are above Bev, so Bev is the worst among three PGs? Depend on which data you use, you will come to different conclusion.

  • shirtless says 7 months ago

    If I'm reading it correctly, Bev gets a much higher offensive rating than Lin. That seems counterintuitive--am I missing something?

    Thanks for this very interesting post!

    Let's also remember that this is a chart based on an average of all players at that position, but once you pull out the dunk-only guys and the PF's there are only three legit centers who rank higher than Howard offensively. Meaning that Howard is actually ranking very well amongst his peers. I mean, any chart that ranks Robin Lopez as the #1 offensive center in the league needs to be looked at with a discerning eye. It's a team stat.

    I think these are two excellent points of conversation. As someone who obsesses over stats and data, arguably my number one rule is to never trust one piece of information too much. All data tell different stories. It's important to look at a great variety of information to better understand a situation, and also to have a grasp on what each piece of information communicates.

    Regarding offensive and defensive ratings, it is very much a team related stat. That's why, in a previous post, I looked at individual ratings relative to team ratings. In this post, I'm looking at individual ratings relative to other players of the same position. Again, two different pieces of information that flesh out different parts of the same situation.

    The four players I quoted above are good examples of why looking at lots of information is necessary. When we look at, say, Beverley and Lin play, we see two very different playing styles. Lin appears more offensively aggressive than Beverley. If my life depended on one of them driving to the basket, I'd choose Lin. Offensive rating, however, is not a measure of how good someone is at driving to the basket. It's points per possession. Considering Lin's higher turnover rate, usage rate, and who might be on the floor with him, it's understandable why possessions with Lin on the floor might result in fewer points on average than Beverley. It does not mean Beverley is a better offensive player; he's just playing a different game.

    The same can be said for Howard. If my life depended on either he or Robin Lopez posting someone up and making a jump hook, I'd choose Howard. But Howard also has a higher turnover rate, usage rate, and much lower free throw percentage, whereas Lopez plays with more knock down three point shooters. Howard is trying to initiate, while Lopez is just trying not to screw things up. All these considerations matter greatly when calculating points per possessions. Hence, Lopez is leading all centers in adjusted offensive rating whereas Howard is middling. It does not mean Lopez is a better (or the best) offensive center; he's just playing a different game.

  • thejohnnygold says 7 months ago

    "Patrick Beverley’s supposed defensive prowess still does not show up. I’m starting to think that the critics who claim that his defense is more showy than effective are correct." - that is absolutely correct, here is the "Opponent field goal percentage at rim" from NBA.com - http://stats.nba.com/playerTrackingDefense.html?pageNo=1

    Maybe I'm misunderstanding your point, but I look at that and see Beverley doing a decent job.

    Per game Bev is giving up 1 fgm at the rim. He is only allowing 2 attempts per game. To me this says two things. First, Dwight Howard helps. Two, his guy is either being forced to pass it off or jack up jump shots (which we like). What else do we want? He can't go Johnny from Cobra Kai on every player :lol:

    sweep-the-leg.jpg

  • p453833 says 7 months ago

    "Patrick Beverley’s supposed defensive prowess still does not show up. I’m starting to think that the critics who claim that his defense is more showy than effective are correct." - that is absolutely correct, here is the "Opponent field goal percentage at rim" from NBA.com - http://stats.nba.com/playerTrackingDefense.html?pageNo=1

  • thejohnnygold says 7 months ago

    Jatman20...about all I can agree with is we need to raise our 3pt%....other than that I'm left a little bit :huh:.

    Does Harden trust Lin? Well, since half the Rockets' fan base doesn't trust him to not turn the ball over it's a good question...until you think about it. It wasn't that long ago Harden passed to Lin for a game-winning shot (the now infamous toe-on-the-line shot). Would Lin's numbers be better if he was the #1 option on a different team and his usg% was 25+? Obviously. Now, if you consider that "prospering" then I guess that's fine, but let's be realistic. If Lin is your best player, and #1 option, you are probably a lottery team. Sorry. Let's just move on.

    As for Howard being a 3rd star? Who the heck are we bringing in better than Howard? That is a short list. Go back to Li's chart. Move the slider to "centers" and actually mouse over all the guys who are above Howard offensively. The majority of those guys are strictly dunkers--meaning they get alley-oops, off. rebounds/putbacks, and little dump off passes from dribble penetration. What they don't do is get fed the ball in the post and beat their man to score. Look at the highest offensive ranks--DeAndre Jordan, Robin Lopez, Andre Drummond, Pekovic, and Varejao. The exceptions are Davis, Bosh, Gortat, Bogut, Horford, and Noah.

    Now, let's take a look at that list of exceptions. Davis, Bosh, and Horford are all PF's who can play C, but let's not confuse things--they are PF's. Gortat and Bogut are legit centers with offensive skills and Noah is very smart and plays within himself. Also, only Bogut is significantly higher on the graph than Howard. Gortat and Noah are only slightly higher than Howard--all three are essentially average. Brook Lopez is probably the best offensive center in the league, but he is out for the year.

    Let's also remember that this is a chart based on an average of all players at that position, but once you pull out the dunk-only guys and the PF's there are only three legit centers who rank higher than Howard offensively. Meaning that Howard is actually ranking very well amongst his peers. I mean, any chart that ranks Robin Lopez as the #1 offensive center in the league needs to be looked at with a discerning eye. It's a team stat.

    Only Horford and Davis are in similar positions on their respective teams where they are asked to lead the offense at times like Howard is. Everyone else feeds off of other, better, players.

    Getting back to three pointers--Howard would be much higher on that list if our guys were knocking down their shots from outside. The same would be true if Howard made 2-3 more free throws a game. If Houston scored 3 more points per game (or 100 possessions) they would be #1 in the league in off. efficiency. Basically, 1 more three pointer or some free throws from Dwight.

  • sli says 7 months ago

    Wow a geek's dream :) Thanks for the charts!

  • kevingan says 7 months ago

    If I'm reading it correctly, Bev gets a much higher offensive rating than Lin. That seems counterintuitive--am I missing something?

    Thanks for this very interesting post!

  • Buckko says 7 months ago Agreed and harden>Bosh but I really like bosh and if we did go for a 3rd star. I would say he is the best bet. Fantastic defender, good rebounder, great jump shooter and not really new to the #3 in a BIG 3.
  • timetodienow1234567 says 7 months ago Howard >>>> Harden so........
  • Jatman20 says 7 months ago

    Give it up......throw all the stats out. Harden with Toronto (excellent 3P shooters and FT shooters) or Thunder who have solid core of guys who have played together for years ( Ibaka, Durant, and even the terrible Perkins)....you have different numbers from Harden. Harden is our closest thing to LeBron (top star) and D12 is like Bosh (distant 3rd star due to lack of post skills and poor FT%). We lack that 2rd star (Morey recently said we lacked that 3rd star).


    Stats are a good baseline; but we have to factor in different accessory parts, different schemes, different talent levels. Does Harden trust Lin....probably not. Does Harden trust Carmelo....maybe. Harden has been with team USA as has Melo. They were forced to share while working with coach K. Does Lin prosper being the alpha dog on his own team? Probably......like Harden had to do to get out of the shadows of that ball dominant Westbrook. The 3 point shooters are not knocking down the 3's (other than Parsons) when our facilitators penetrate.......Olajuwon would look as bad if Horry, Mad Max, Jet,

    Mario E-junk yard dog don't make their 3's. one vs five.

    Today's help defenses are better now-a-days....back then they left you on an island. Pacers and Miami are so long and athletic that they just switch on screens and pick n rolls. A Harden/Melo ( both are 85% FT shooters) PnR would be awesome; while Harden/Lin doesn't scare the elite teams....especially when 3Pt's have been slumping for over a month.


    And what happens when a team zones us and eliminates all sets? Dallas won a championship zoning the Heat.......3 point shooting zone busters are a must. Dallas has zoned us twice this year and we lost both contest. The theme here is better 3 point shooters. Garcia is rumored as of today to be trade bait. A slump for a week or so is one thing.....but more than a month hurts.

  • shirtless says 7 months ago

    Defensive and offensive rating are points per 100 possessions. A player's offensive rating equates to how many points his team scores per 100 possessions during which the player is on the floor. A player's defensive rating equates to how many points his team's opponent scores per 100 possessions during which the player is on the floor. Steals, blocks, assists, and other such stats don't factor into the formula at all.

    @thenit Depth only matters in as much as it affects the average for the position. So if you are an OK player, but every other player at your position is amazing, you come out looking like a bad player. Alternatively, if you are an average player, but every other player at your position is awful, you come out looking like a good player.

  • BrentYen says 7 months ago

    I think TTNN explained it above.

  • John P says 7 months ago

    I don't get this entirely. Beverley, according to my completely non-expert eye adds value by hustle, fire, and harassing D....yet his offense is ranked as OK? Other teams play off of him and dare him to shoot 3's recently. I get that you are comparing PGs to PGs....but still just a gut check seems to tell me something different. ...also Harden has good D? I am pretty sure that is wrong...and at least compared to Beverley his D should be worse not better. Anyway, thanks for the article and all of these that you do. A great way to look at the game.

  • thejohnnygold says 7 months ago

    Haha--the Knicks and Lakers!

  • TTNN says 7 months ago

    oh, yeah, regarding the position differences in defensive rating, as I said, since the numbers were contributed only by blocks, rebounds, and steals etc. So positions who generate big numbers in those categories will for sure have better defensive ratings, such as centers and PF, who tend to have more rebounds and blocks than guards.

  • TTNN says 7 months ago

    If you look at how the defensive ratings are calculated, you would realize that the 80% of it were determined by the team performance, rather than individual performance, because,....... it is "team defense". And your example of Pacer vs. Bucks clearly shown that. As individually, I'm sure the best defensive player on Bucks should be better than the worst defensive player in Pacer, however, as the concept of team defense, if the team is no good at defense, there is really limited for each player could do.

    And then for the rest 20% which comes from individual player's performance, that was not calculated on how much your opponent scored, but rather calculated purely by numbers comes from blocks, steals, and rebounds, and fouls. (as fouls generate a stop of the offensive flow thus was included as a positive factor there.) Thus if you denied a jump shot, or you let your opponent blown by with no effort in stopping it, those would have no impact on your defensive rating, that would affect the whole team's defensive rate only. That's why James Harden's defensive rating is not bad. Beverley would not be bad also because he is good at rebounding and steals, but I don't think this parameter completely reflect the defensive capability of our player there.

  • thenit says 7 months ago

    Interesting, I would agree on Bev and Lin, they are about average. Bev looks better due to his "flashiness" more than substance, because he is all over the court. Lin's weaknesses we already know. However in their defence, the NBA is stacked with great PGs. In most teams their best offensive guys are the PGs especially in the west. While the depth at SF, SG and C are not as deep.

    Richard I'm not as literate in math and stats as you but does depth in a position play a role in your graphs or is it the average of the position play a larger role?