Expected Effective Field Goal Percentage: 2018-19 Postseason Recap

Kirby Lee – USA TODAY Sports

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.

After the end of the regular season, I went over the final XeFG% results (offensive and defensive) for the season in this article. Now that one of the most exhilarating and memorable postseasons in recent memory has come to an end, we can now take a look at the best offensive and defensive performers from the 2018-19 NBA playoffs.

If you would like to see if players overperformed or underperformed compared to the regular season, you can easily find data for the past regular season under the NBA tab on the site’s navigation bar.

Offensive Efficiency

The first thing that sticks out to me is that the data points appear to be more heavily concentrated underneath the expectation curve. In the regular season, this is obviously not the case because the entire purpose of the expectation curve is to represent an average player — an uneven distribution wouldn’t make any sense. However, it does seem logical to imagine that scoring in the postseason is not quite as easy as it is in the regular season due to players putting forth more effort defensively. I could have calculated a new expectation curve for the postseason, but I think it’s useful to see this shift and particularly to observe which players suffer the most (and the least) from this increase in difficulty in the postseason.

For example, Golden State’s legendary scoring trio of Stephen Curry, Klay Thompson, and Kevin Durant all dominated the XeFG% rankings for the 2018-19 regular season. Durant and Thompson mostly maintained their superb efficiency, but Curry went from shooting 8.97% above expectation to shooting just 3.44% above expectation. This is obviously still excellent, but it’s still a huge decrease from what we have come to expect from the greatest shooter of all-time. Of course, maybe it’s not fair to compare his performance to Durant’s and Thompson’s. Durant averaged over 34 PPG before he suffered a calf injury against the Rockets in the second round, while Thompson would have been a great pick for Finals MVP if he was able to remain healthy and lead the Warriors to a championship.

Donovan Mitchell’s efficiency was horrible, but his position on the Jazz is extremely difficult to succeed in for a 22-year-old player. The Jazz could really benefit from putting another scoring threat alongside Mitchell, such as D’Angelo Russell, who was in a similar position on the Nets.

One underperformer without an excuse for his horrible play is Russell Westbrook. Instead of allowing Paul George to build upon an extremely impressive 36-point performance in Game 5 against the Trail Blazers, Westbrook dominated the ball in crunch time and took bad shot after bad shot. We’ve come to see this far too often from the former MVP and it may have even been a factor in Durant’s departure from Oklahoma City.

Speaking of disappointing elite guards, fans were waiting all season for Kyrie Irving and the Celtics to step up their game in the postseason but it never happened. Take a look at Irving’s FGM-FGA splits after winning Game 1 of the second round against the Bucks: 4-18, 8-22, 7-22, 6-21. Those were his final four games of the season, and it’s looking increasingly likely that they will be his final four games wearing green for the Boston Celtics. Not a great way to go out.

I’m sure Portland Trail Blazers and Milwaukee Bucks fans are hardly surprised to see Al-Farouq Aminu and Eric Bledsoe far below the expectation curve. Both players severely underperformed for their teams. Fortunately, Rodney Hood and George Hill stepped up to the plate for their respective teams. Hood subbed into a quadruple-overtime game against the Denver Nuggets to nail a game-winning shot, while George Hill upped his scoring averaged from 6.8 PPG (49.3 eFG% in the regular season to 11.5 PPG (61.9%) in the postseason. Unfortunately, Bledsoe is the one signed to a long-term contract.

Speaking of the Milwaukee Bucks, it was a disappointing end of the season for the likely winner of the league’s Most Valuable Player award: Giannis Antetokounmpo. Giannis actually finished below the expectation curve despite an easy first round matchup against the Detroit Pistons. Antetokounmpo enjoyed a stellar regular season, but the best player in the East might be the guy who rested to focus on staying healthy for the postseason and ended up winning Finals MVP.

I chose to include an additional visualization for the purpose of comparing these postseason offensive performances to their regular season counterparts. The slightly transparent dots represent the regular season, while the completely filled dots represent the postseason.

As previously mentioned, you can see that Klay Thompson and Kevin Durant improved upon their regular season shooting efficiency while Steph Curry faltered. Giannis Antetokounmpo, D’Angelo Russell, Donovan Mitchell, Joel Embiid, Kyrie Irving, Pascal Siakam, and Russell Westbrook all experienced significant regressions as well. Ben Simmons surprisingly improved even though he’s the one who’s consistently called a liability in the playoffs. Finally, a few players remained consistent. Kyle Lowry, Damian Lillard, and Jimmy Butler all displayed a minimum change in performance, and both of Kawhi Leonard’s data points are basically on top of each other.

Defensive Efficiency

Once again, most of the players are located below the expectation curve. However, a spot on underneath the curve is actually a positive thing when talking about defensive efficiency because it means a player allowed their opponent to score less efficiently than expected. As previously explained, scoring becomes more difficult in the postseason, so this accounts for the observable shift in the data.

Another statistical dilemma with the postseason is the extremely small sample size and the fact that a larger chunk of that sample size is spent playing against the same players. For example, take a look at Damian Lillard’s placement below the expectation curve. I would argue that Lillard is an underrated defender and isn’t as bad as some other elite guards, but he’s also not that good. So, why is he placed so low (or high, depending on how you look at it)? Well, a large portion of his defended shots were from Russell Westbrook, who was offensively horrible this postseason. Did Lillard do a good job at defending Westbrook? Well, he was certainly passionate while doing so. However, I think Westbrook’s offensive woes were a product of his own flaws, not Lillard’s defense on him. Over the course of an 82-game season, Lillard would have defended against many different players, so a few bad games from Westbrook wouldn’t make a difference. In the postseason, this is not the case.

The same problems with shooting-percentage-based defensive metrics hold true here. A team’s best defensive players tend to guard the other team’s better offensive players, while the worst defensive players tend to be hidden on their less offensively-competent opponents. Take a look at Klay Thompson. He’s widely regarded as one of the league’s best perimeter defenders, yet he actually performed worse than expected in the postseason. Is he actually overrated? That’s a possibility, but the eye test supports the fact that he’s a stellar defender. So, let’s take a look at the players who he had to guard this postseason: Lou Williams, James Harden / Chris Paul, Damian Lillard / CJ McCollum, Kawhi Leonard. It suddenly becomes a lot more understandable why Klay’s defensive numbers aren’t great.

While I don’t think Klay’s placement on the graph disproves his reputation as an elite defender, the opposite might be true for Enes Kanter. Kanter earned a reputation as a defensive liability during his time with the Thunder, but he thrived when called upon by the Trail Blazers after Nurkic went down with a devastating season-ending injury. Kanter didn’t have any easy matchups either — he was the primary defender against Steven Adams in the first round and Nikola Jokic in the second round. Kanter wasn’t the only Portland big man to perform extremely well on the defensive side of the ball. Zach Collins made a name for himself at Gonzaga with his extraordinary shot-blocking ability, and it has certainly translated to the NBA. Collins’ rim-protecting presence was so important against Denver’s duo of Paul Millsap and Nikola Jokic and was a huge factor in Portland’s eventual triumph.

I previously mentioned Giannis’ disappointing performance on offense, so it’s only fair that I point out his ability to maintain his DPOY-level play from the regular season. The Greek Freak didn’t have any easy matchups against the Celtics or Raptors, but he held his own, which is extremely promising for a player of his age. His offensive game currently suffers from one-dimensionality, but it’s not hard to imagine him becoming the best two-way player in the game.

Finally, I wanted to throw a shoutout to Myles Turner. I’m a fan of Turner’s game and I believe he’s extremely underrated for his dominance on the defensive side of the ball. He isn’t on the graph because the Pacers were swept in the first round by the Celtics so none of their players qualified, but Turner allowed an effective field goal percentage of 42.86% while he was expected to allow an effective field goal percentage of 54.39%. Would he have maintained that unbelievable differential over a larger sample size? Probably not, but it’s certainly incredible nonetheless. Turner recently turned 23-years-old — this level of defensive prowess is extremely rare for his age.

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