Who Protects the Basket?

Over the last few months, Omer Asik has been involved in lots of trade discussion. However, the question to most fans is why would a team want to trade for a player that has career averages of 5 points and 7 rebounds? The analytically savvy may be aware of Asik’s worth on defense, but how do you quantify it? Here’s another question: with 2 bigs who are so-called rim protectors, which one of the Rockets’ big men is actually better? Before screaming “Dwight,” continue reading below.
In a previous article, we looked at the value of contesting shots. However, rim protection entails more than just contesting shots. We need to look at how often the defender blocks shots as well. Together, by combining a player’s contest/altered frequency with his blocks frequency, we can develop a rim protection rate statistic. So who is protecting the basket?

We can look at this a few ways. First, rather than just presenting a table of information, let’s look at rim protection in the form of a heat map.

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We see some interesting if not completely surprising names here. Brandan Wright has long been a per minute star, averaging a 21.2 Player Efficiency Rating over the last 2 years. He also finished with a 2.2 xRAPM last year and was on the plus side in the previous year. After missing the first 23 games with an injury, Wright is back and playing well. However, the assumption with Wright has long been that he’s too thin to muscle with the big boys down low. Yet, despite his skinny frame, he has a long wingspan that is able to help him block an above average amount of shots and contest whatever he doesn’t block. If Wright is able to stay healthy, he’s a player to keep an eye on.

We see that Asik is one of the better rim protectors as well. In fact, we see that he protects the rim at a better rate AND allows a lower FG% at the rim on those contested shots than Dwight Howard. As has been mentioned in many rumors surrounding Asik, the Rockets are actually better defensively when he is on the court then when Dwight is. Does this mean Houston is trading away the wrong center? That would be taking it a bit far — Dwight is still much better offensively and while he hasn’t been as good as Asik at protecting the rim, he isn’t chopped liver either.

Brook Lopez finished with the highest Contest+ so it is not surprising to see him leading the way in rim protection. While he only blocks shots 0.6% more than the average big man (PFs and Cs), he is able to get his hand up and at least contest or alter most shots.

When I first ran the numbers in the previous article for contest frequency, I was surprised to see Serge Ibaka with a relatively low contest/altered frequency. Alas, it was only because he was too busy blocking nearly 25% of the shots attempted against him near the basket!

However, perhaps the biggest surprise on this list is Tyson Chandler, the one time DPOY. With a 45.8% rim protection rate, he comes in as one of the worst players in our sample and worse, he is 8% worse than the average big man which you can see visually with the “cold” blue box.

One thing I’m sure we all noticed when looking at rim protection rate is that many of the names we would expect to see at the top are actually not at the top. So are guys like Roy Hibbert, Tim Duncan, and Marc Gasol not as good as we expect? Is rim protection rate perhaps misleading? Is rim protection FG% actually the better statistic? It’s hard to answer the last question without having a larger sample size and observing how both rim protection rate and FG% vary over time. However, we can plot rim protection rate vs. rim protection FG% to see if there are significant differences.
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Well that is pretty messy. The correlation coefficient is actually not as bad as the graph looks (-0.26) and the fact that the two statistics are negatively correlated is certainly a good thing — i.e. as rim protection rate goes up, rim protection FG% should go down. Theoretically at least. Still, it’s not a very strong correlation and leaves us asking the question, Which of these metrics is stronger in predicting a team’s defensive efficiency?
We also have one other metric we can look at: close frequency. What is close frequency? It is the percentage of a player’s shots defended that came near the basket. We can get an idea of which players are always near the basket and which players wander around a bit more and are guarding shots further away from the hoop.
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In the graph above, the players with larger bubbles are guarding a higher percentage of their shots near the basket. We see that some of the past DPOYs like Marc Gasol, Tyson Chandler, Tim Duncan and perhaps this years DPOY Roy Hibbert do not have the largest bubbles. The percentage of shots they have defended near the basket range from about 60%-65%, which means that about 35%-40% of the shots they have defended are at mid-range or near the 3 point line. Of course, with the 3-seconds-in-the-paint rule, no one can maintain a 100% rate here because ultimately you have to leave the paint. In the future, we will look at the distribution of each player’s shots defended along with his defensive usage (Vantage tracks shots defended per chance). We can also use the distribution of shots to develop an expected points per shot metric.
For now though, we can see which players are near the basket the most (close freq), which players attempt to protect the basket (RP rate) and which players successfully protect the basket (RP FG%).
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Finally, as a refresher, it’s worth visually seeing what the difference between getting an open shot under the basket versus if that shot is contested:
Almost every player in the league allows a higher FG% when the shot is open versus if it is contested. And we can see a clear difference between the two types of shot defenses.