Expected Effective Field Goal Percentage: 2019-20 Quarter Season Recap

Brad Rempel – USA Today Sports

Last season, I introduced Expected Effective Field Goal Percentage (XeFG%). In short, the statistic predicts the effective field goal percentage (eFG%) a league-average player would have if they attempted the same shots as any given player. A player with a high XeFG% takes high percentage shots, while a player with a low XeFG% takes low percentage shots. The purpose is to add context to traditional shooting metrics like effective field goal percentage. Instead of simply taking a player’s eFG% at face value, you can compare it to their XeFG% to see whether they are performing above or below expectation. For more specific details about XeFG%, including how it’s calculated and its flaws, you can read the initial article explaining it here.

I posted an article last week documenting how XeFG% can be quickly calculated with Python. We’re nearing the quarter season mark of the 2019-20 NBA regular season, so I thought I would put the code to use. One decision I made was to use the 2018-19 NBA season average field goal percentages to determine ‘expectation’ because of the larger sample size. Everything else is the exact same as my past article.

Offensive Efficiency

The four eligible players furthest below the expectation curve are RJ Barrett, Coby White, Mike Conley, and Russell Westbrook — two lottery picks and two seasoned veterans.

Conley’s scoring efficiency has taken a crazy hit. Last season, he averaged 21.1 PPG with an eFG% of 50.7%. Through 18 games this year with the Utah Jazz, his PPG is at 14.3 and his eFG% is a measley 44.1%. While his 3P% has dipped (36.4% to 34.7%), the biggest decline is in his 2P% (48.3% to 38.3%). Part of this may be due to Rudy Gobert being a far less versatile big man on the offensive end than Conley’s former Grizzlies teammate, Marc Gasol. Gasol’s ability to stretch the floor gave Conley more room to work with. Conley’s a crafty player who can use space to create an efficient floater, but when Gobert sets a pick, everybody on the floor knows he’s going to roll to the basket. Or maybe Conley’s finishing has simply regressed, who knows?

Conley’s inefficient scoring surprised me. Meanwhile, I would have been surprised if Westbrook wasn’t this inefficient. He has steadily regressed every year since winning MVP in 2017. It’s sad seeing his offensive flaws exposed on the Houston Rockets because Chris Paul was so perfect for that offense. If I’m playing the Rockets, I’m double teaming Harden and forcing Westbrook to make a play. That might be the plan.

Finally, there’s the two rookies. It’s not terribly worrisome for a player to be inefficient in their inaugural season, especially because lottery picks tend to belong to bad teams which isn’t the best situation to be thrown into. Last year, XeFG% rated Trae Young and Luka Doncic poorly. Now, they’re playing like superstars. Of course, then there’s Collin Sexton who has become even less efficient. We’ll just have to wait and see which direction White and Barrett take, although I’m not terribly high on either player.

Anyway, enough with the under performers. The two most obviously efficient players compared to expectation are Karl-Anthony Towns and Devin Booker (who happen to be very good friends).

Towns’ three-point shooting has been absolutely absurd. He’s taking 8.9 treys per game, up from 4.6 last season — and he’s nailing 44.4% of them compared to 40.0% last year. As a result, he’s taking the least amount of two-pointers in his career. That’s fine when he’s hitting shots at this rate, though — he’s never been this efficient.

Booker is taking 17.3 shots per game, the lowest average of his five-year career except for his rookie season. It’s also by far the most efficient scoring season of his career. His 2P%, 3P%, and even his FT% are all up by significant margins. Booker’s 52.1% eFG% last year was his career-high at the time. This year, he’s at 58.2%. So, what changed? Booker’s touches are down. He’s not expected to carry the entire offense. The Suns have an actual point guard in Ricky Rubio who can bring out the best in the rest of the team, including Booker. It’s been clear for quite some time that Booker is one of the absolute best scoring talents in the league, and now his talent is being properly utilized. With Rubio, Booker, Ayton (well…), Oubre, and Baynes, the Suns are looking pretty damn good.

Here are a few sleepers. LaMarcus Aldridge is quietly playing exceptionally well at 34-years-old. His playstyle, which is predicated on the mid-range jumper, is going out of style, but he’s certainly not the reason for it. Bojan Bogdanovic is in nearly the same spot he was last year — incredibly consistency despite changing teams. And Kendrick Nunn is putting up 16.5 PPG with an eFG% of 56.5% as undrafted rookie. That’s insane.

Defensive Efficiency

Quick disclaimer: I believe that my newer defensive metric, Defensive Points Saved (DPS), is better at quantifying defensive performance than DXeFG%. But I’ll provide DXeFG% anyway because I don’t think it’s entirely useless. Also, the code for calculating DXeFG% is different than the code I posted here on calculating XeFG%. I don’t think it’s worth creating a new article and the method is very similar so including it in the same article would be very repetitive, so here’s just a link to the full code for calculating DXeFG%.

Anyway, on to the actual results. Remember that good defenders should be above the expectation curve, while bad defenders should be below the expectation curve. Most of what we see meets the eye test. Players like Rudy Gobert, Jonathan Isaac, Anthony Davis, Bam Adebayo, Karl-Anthony Towns, and Jrue Holiday are all appropriately recognized as top defenders. Meanwhile, players like Kemba Walker, Cody Zeller, and Bradley Beal deserve their labels as poor defenders.

However, there are obviously a few surprises. For one, it looks like DXeFG% absolutely hates Danny Green for some reason. He’s known as one of the best defensive guards in the NBA. DPS gives him credit, plus/minus metrics like D-PIPM give him credit, the media gives him credit, etc. But this year and last year, DXeFG% labels Green as a very bad defender. Odd. On the other end of the spectrum, CJ McCollum is actually rated as the most efficient defender in the league so far this this season among eligible players. Now, I’m higher than most people on CJ’s defense. Many people act as if he’s a liability, but I think he’s just slightly below average on that end of the floor. Certainly not the best defender in the league, though!

There’s plenty of more things to analyze, but I’ll leave it at that. You can see the XeFG% data here and the DXeFG% data here. In the past, I’ve also maintained individual and team data, but I’ve found that team XeFG%/DXeFG% is pretty useless and not worth the time, so I’m no longer going to post or update the metric for each team. As always, the full player data will be in the XeFG% and DXeFG% tabs under ‘NBA’ on the site menu.


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