Expected Effective Field Goal Percentage: 2018-19 Season Recap

USA Today

Earlier this 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.

Let’s dive into the final calculations for the 2018-19 regular season. All of the graphs below only include qualifying players for the sake of clean data visualization. For the full sortable data, you can use the website’s navigation bar to find the XeFG% and DXeFG% links under the NBA tab.

Offensive Efficiency

Most of the results make intuitive sense. For instance, Kevin Durant, LaMarcus Aldridge, and Demar DeRozan all have a low XeFG% because they tend to shoot more mid-range jumpers than the average player. On the other side of the spectrum, Andre Drummond, Julius Randle, and Giannis Antetokounmpo primarily reside in the paint, which explains their high XeFG%. These different names obviously experience varying levels of success. A “bad” shot selection for Durant isn’t actually bad — he’s a seven-footer with a guard’s handles who can get his shot over anybody at any spot on the court.

The majority of the league’s best players are located above the expectation curve, which means that they hit more shots than a league-average player would. That’s why it’s initially surprising to see Joel Embiid below this line. He’s one of the most dominant post players in the league; how could he have an effective field goal percentage below expectation? Well, it’s actually less surprising when you look at his shooting splits. Instead of being closer to the right side of the graph with the other big men, he’s in the middle for a reason — Embiid shoots too many threes. He’s pretty awful at it. Among players with at least 250 three-point attempts, Embiid has the 2nd worst three-point percentage despite being left wide open at the third-highest frequency. In other words, an incredibly high amount of Embiid’s three-pointers are wide-open, which drives up his XeFG%. However, he misses most of these wide-open shots, so his effective field goal percentage takes a hit. Embiid being too eager to take the jumpers defenses hand to him often led to trouble for the Sixers offense (see: Game 1 of the first-round series versus Brooklyn). When he avoids these shots in favor of utilizing his biggest strengths near the basket, it’s very hard to contain him and the rest of the Sixers (see: Game 2 of the first-round series versus Brooklyn).

I would be lying if I said I was surprised to see Westbrook below the expectation curve. He’s having an awful season in terms of shooting efficiency (and he’s already set the bar pretty low). Westbrook’s shooting splits are down across the board and he’s never been the most efficient player in the first place, so that’s not a great sign. Fortunately, Paul George has been playing at an MVP level for the Thunder.

Defensive Efficiency

There are a lot more players who are worth including in this data visualization, so I’ll have two graphs in this section. The first chart includes players who defended at least 900 shots this season.

First, I should mention that there’s one major flaw in individual defensive metrics based on an opponent’s shooting percentage. The matchups in a game are adjusted based on the defensive capabilities of various players. You want to hide your worst defenders against lesser offensive players while your best defenders take on the other team’s main scoring threats. Positions and body build obviously matter, but that’s the general idea. Why does this matter? Well, in the graph you can see that Jrue Holiday is above the expectation curve (which is bad on defense). Holiday is one of the league’s best perimeter defenders — that doesn’t make sense. Well, the Pelicans match him up against the other team’s best perimeter players, which the statistic cannot account for. This isn’t too important for the offensive version of the metric, but it’s very significant on defense.

In many cases, this matchup dilemma can easily explain any discrepancy. In other cases, it may not be a valid excuse. Danny Green is recognized as one of the league’s best defensive guards, yet he’s well above the expectation curve. While he’s also matched up against good offensive players on the other team, the Raptors also have another great perimeter defender on the team — Kawhi Leonard. Plus, Green isn’t just barely above the curve like Holiday. There’s a massive gap which suggests that Green hasn’t been doing the best job defensively. He was actually well below the expectation curve in 2017 when he earned a spot on the NBA All-Defensive Second Team, so this doesn’t mean that he was always an overrated defender or anything like that. Nothing conclusive can be said, obviously.

With that being said, let’s look at some of the other results. Most of the names furthest below the expectation curve are well known for their aptitude on that side of the ball — Jusuf Nurkic, Joel Embiid, JaVale McGee, Rudy Gobert, and Myles Turner are some of the league’s premier rim protectors. It’s a bit surprising to see Karl-Anthony Towns and Nikola Jokic on the bottom side of the graph, though. They’re typically viewed as some of the league’s worse defensive big men, yet they’re apparently above average in terms of shooting percentage allowed above expectation. On the other hand, Towns’ teammate Andrew Wiggins is on the wrong side of the expectation curve on offense and defense. Don’t look at his contract, T-Wolves fans.

Next up, we’ll take a look at the qualifying players who faced less than 900 shots this season. Again, use the website’s navigation bar at the top of your screen to browse underneath the NBA tab for the full sortable and specific data.

If you’re a fan of Trae Young, Luka Doncic, or Collin Sexton, this article probably wasn’t very enjoyable for you. The three rookies finished on the wrong side of the expectation curve on both offense and defense. Sexton in particular really dragged out the y-axis single-handedly, which is actually rather impressive (in a bad way, of course). Once again, it’s not surprising to see some of the names at the bottom. Kevin Durant, Klay Thompson, Ben Simmons, Anthony Davis, and Hassan Whiteside have all been praised for their defensive talent. Giannis Antetokounmpo is living up to his Defensive Player of the Year contention with his placement on the graph.

Jayson Tatum is an interesting case. He’s obviously a very young player, but he has displayed a lot of promise on the defensive side of the ball. On offense, you may have noticed that he was below the expectation curve. Tatum’s shot selection has deteriorated in a season in which most fans hoped he would exhibit more growth on that end of the floor. If Tatum can improve his decision-making on offense, the 21-year-old will already be a very formidable player in the NBA.

In case you want to know where players like Antetokounmpo, Whiteside, and Sexton would be located in the previous graph, here’s a combined version of the two visualizations.

Yeah, Sexton is not a good defender. Our data goes back to the 2013-14 NBA season and since then, no player has defensive efficiency numbers versus expectation as bad as Sexton’s on the same volume.

In conclusion, I think using expected effective field goal percentage is a good way to contextualize traditional offensive and defensive shooting metrics. Don’t believe me? Look at the last defensive graph I included and notice that Eric Bledsoe and JaVale McGee both allowed an effective field goal percentage just below 50%. That’s a bit misleading, though. The graph shows that considering the types of shot McGee faces as a center, allowing an effective field goal percentage of just below 50% is far better than average, while it’s basically average for Bledsoe.

More context is always a good thing.

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