Comparing the Goalkeeping quality in Europe's Top 5 Leagues. Finding evidence for 'Bundesliga Tax' amongst German goalkeepers?

This is a data-driven article on goalkeepers. All the data mentioned here has been collected from www.fbref.com.

We all love comparing things in life. Football is no exception. Fans compare their favorite player to another, the team they support to another and even the leagues they follow.

Data makes this a lot easier. In fact, in the last five years, the football data industry has taken a leap to the point where we have data for almost all on-ball actions. In this article, I try to analyze the goalkeeping quality in Europe's Top 5 leagues using data.

First, I'd like to introduce the metrics that I'll be using during the course of this analysis. Let me first introduce the expected goals (xG) metric which determines the probability of a shot ending up as a goal regardless of the actual outcome, thus eliminating the 'finishing quality' factor that would vary from shooter to shooter.

The post-shot expected goals (PSxG) uses information available after the shot has been taken, which includes the shot's trajectory, speed and other factors which aren't taken into account in the xG model. Thus, not every attempted shot receives a PSxG value, only the ones that end up on-target do.

Hence this can be used to determine how good a goalkeeper's shot-stopping ability has been.

Shot Quality is measured as PSxG per shot on target (PSxG/SoT). The higher the value, the tougher it was to save the shot.

I've used the PSxG data from the last three completed seasons i.e, from 2018/19 to 2020/21 for this analysis.

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Goalkeepers' performances across the top 5 leagues

La Liga

La Liga has some great goalkeepers in Atletico Madrid's Jan Oblak, Real Madrid's Thibaut Courtois, Athletic Bilbao's Unai Simon and FC Barcelona's Marc-Andre Ter Stegen. But how did the league perform during the concerned seasons? Let's find out.

In 2018/19 La Liga goalkeepers had a PSxG-Goals allowed (GA) value of +1.215 for a Shot Quality (SQ= PSxG/SoT) value of 0.29. This means the average goalkeeper in the league has saved 1.215 more goals than expected, according to the PSxG model.

In 2019/20 the PSxG-GA value was -1.01 for a Shot Quality value of 0.287. This means the average goalkeeper conceded almost a goal more than what they were expected. The 2020/21 season also ended in a net negative impact where the PSxG-GA value was -1.18 for a slightly better Shot Quality value of 0.3.

In conclusion, for the 3 seasons we considered, the average PSxG-GA value was -0.325 for a Shot Quality value of 0.292. This implies that the La Liga keepers underperformed.

Bundesliga

The Bundesliga features one of the greatest goalkeepers of the 21st century, Manuel Neuer. But what was the overall performance of the league's goalkeepers?

In 2018/19, Bundesliga goalkeepers had a PSxG-GA value of -2.26 for a Shot Quality value of 0.307. They continued to under perform for the next two seasons too. In 2019/20, the PSxG-GA value was -2.62 for a Shot Quality of 0.31 and in 2020/21 it was -2.38 for a Shot Quality of 0.3.

Overall, for the 3 season sample, the Bundesliga goalkeepers performed the worst, having a negative PSxG-GA value of -2.42 for a shot quality value of 0.307. They were the worst performers among the top 5 leagues and almost by a fair distance.

The difference between the 4th placed league and Bundesliga was almost -1.2. Or the Bundesliga having conceded 1.2 more goals than the 4th placed league. Wait, did we just find evidence for "Bundesliga Tax"?

Premier League

In the summer of 2018/19, the Premier League broke the transfer record for the most expensive goalkeeper not once, but twice. First, when the current Liverpool shot-stopper Alisson Becker made his move away from AS Roma. Then the current record-holding transfer happened when Chelsea bought Kepa Arrizabalaga from Athletic Bilbao for a reported €80 million fee.

In 2018/19, the Premier League recorded a PSxG-GA value of +0.14 for a shot quality value of 0.31. They continued to over perform and improved their values in the following seasons. In 2019/20, the PSxG-GA value was +1.05 for a shot quality of 0.31 and in 2020/21 it was +1.56 for a Shot Quality of 0.3.

Overall, the Premier League goalkeepers saved 0.92 goals more than expected for the three seasons when the shot quality was a good 0.307. They were the only league among Europe's Top 5 leagues to record a net positive value during the three seasons.

If you're looking for good goalkeepers, the Premier League is the league to watch.

Serie A

In 2018/19, the Serie A goalkeepers recorded a negative PSxG-GA value of 0.3 for shot quality of 0.278. In 2019/20, they improved, having a PSxG-GA value of +0.175 for a shot quality value of 0.284.

But in 2020/21, Serie A goalkeepers recorded the worst performance for a single season in the three season sample, recording a PSG-GA value of -3.32 for a shot quality of 0.3.

Overall, Serie A goalkeepers underperformed, conceding 1.14 goals more than expected for shot quality of 0.287

Ligue 1

The Ligue 1 was placed 4th according to the PSxG-GA model. In 2018/19, they had a PSxG-GA value of -0.765 for shot quality of 0.278. The trend continued for the following seasons. In 2019/20 they conceded 0.125 more goals for a shot quality of 0.276 and in 2020/21, they concededed 2.805 more goals than expected for a shot quality value of 0.2925.

Overall, the league's goalkeepers underperformed, recording a PSxG-GA of -1.23 for a shot quality of 0.282.

Conclusion

The Premier League was the only league that managed to have a net positive value for PSxG-GA during the three seasons that we considered. La Liga came second, while Serie A finished 3rd. Ligue 1 and Bundesliga came 4th and 5th and both leagues never overperformed their PSxG in any of the three seasons considered.