It has been a little over two weeks since Liverpool's season ended with a painful 0-1 loss in the champions league final. The results in the last week of the season (losing the title to City and then the Real game) made it seem not that great, so as a way to recover emotionally, I decided to use some data and try and get this season and the last 5 years in perspective (hopefully it would make me feel better..)
I have been a fan of LFC for almost 25 years, most of them included mediocre play and less than exhilarating results.
The few highlights were super-high (see the pic here) but since the early 1990's until fairly recently, Liverpool failed to seriously compete with its rivals from Manchester and London. Since late 2015, with the arrival of Jurgen Klopp and a growing investment by ownership, there seem to be different perception of this team – no longer fighting to enter the club of "we are contenders for the EPL title" but actually competing (and winning) all possible titles.
This post reflects on the past season, its uniqueness, and where Liverpool's stands among the best clubs in England and Europe as a whole. I will spend some time analyzing the season that just ended. Then, I'll expand the discussion and explore most of Klopp's tenure and some of the aspects that helped me have a better appreciation for this team.
An ode to 2021-2022
Let's begin with a dry summary and hardware count: two domestic titles (FA and EFL cups), runners-up in the EPL title race (missed by 1 point, more on that later), and runners-up in the CL (a loss in the finals).
While a 4-title season was on the table until relatively late in the year, Liverpool was able to win two domestic cups, almost completed an amazing comeback to win the EPL title in the final week of the season, and then had a heart wrenching loss in the UCL final to Real Madrid.
Such a long season: looking at total minutes load
One central aspect that many have mentioned with regard to this season is the minutes load. The fact that despite high number of games and minutes played, Liverpool remained in contention for all four titles is amazing in itself. The last English team to compete (and win) all titles was 1998-99 Manchester United. That was an amazing accomplishment. For my first "let's put this year in perspective" test, I looked at total minutes and games played by the top-3 players comparing 2021-22 Liverpool with 1998-99 Man. United.
We see that this year’s Iron-men played more minutes than the late 90's group (in some cases substantially more). Directly comparing similar positions - Neville and Alexander-Arnold - the latter played 2 more games but a total of 240 minutes more, which is more than 2.5 additional games.
As part of the quest to win all titles, the ever-present and calm rock of the defense - Virgil van Dijk - played almost 1000 minutes more than David Beckham, who was number 3 on Man. United’s list of Iron-men in 1999.
The last point of emphasis to better appreciate the grueling season that Liverpool just completed is related to the differences between soccer in 2022 versus 1999. The pace, offensive style and focus on quick-passes are dominant in today's game, much more than the late 1990's primarily long-ball style soccer. Unfortunately, pace stats require spatial data which I could not access, so the point needs further analysis (more on pace here and here; at the same time, some contend that the recent tactical innovations are actually slowing the game, see here).
A leader among giants
So, the first thing we've learned is that despite a grueling season, Liverpool had success with 2 domestic titles, and was one supernova game by the Real Madrid goalkeeper from another European title. Speaking of which, for my second point of perspective, I focused on Liverpool's place among the top clubs in Europe.
One of the dominant aspects of modern soccer is the strong push for quick passing, offensive, goal-heavy style. As such, data on scoring is central to any debate about Europe's top clubs. With the explosion of soccer advanced analysis and sophisticated metrics, a central stat is xG (expected goals) which describes the probability that a shot will result in a goal based on some of the characteristics of the shot (like the shooter's location or the type of attack) and the events leading up to it. An important feature of this metric is that it estimates how an average player or a team would perform in a certain scenario (in other words, it is not a specific player's quality that is the issue). xG has become one of the most dominant tools in the analysis of modern soccer as a way to explain and evaluate a team and a player's performance (more details here). The figure below uses data from football reference.com and presents the top-2 teams in Europe's main leagues and their offensive outputs, both actual goals scored (GF) and xG (logos used in this plot are from this repo).
One initial observation points to the dominance of the English premiere league teams (Liverpool and Man.City): both clubs are top-3 in both scoring categories. Liverpool stands tall as number 1 in xG and number 3 in actual goals scored. The strong offensive style pushed by Klopp is evident here (I’ll come back to it in more detail later).
Building on xG and goals scored, another way to compare Europe's top clubs is to look at the difference between both measures. A positive gap (more actual goals scored than expected) suggests that a team performed in a way that is above average in its finishing and shooting ability. A negative difference is indicative of under-performance from an offensive standpoint. The plot below displays the same 10 clubs and highlight the difference of offensive performance.
The figure serves as further evidence for the high quality of Liverpool's season – the team had the highest xG among Europe's top teams, and over-performed that expected value by almost 5 goals. It stayed very close to its English counterpart Man. City, as well as Bayern who dominated the Bundesliga. The small gap between GF and xG points to good execution and taking advantage of opportunities, but also to not a lot of luck. When xG is average and the gap with actual goals is large, it also suggests that a team experienced more luck since some of the shots that were not expected to score actually ended as goals (see Dortmund and PSG).
To balance the offensive picture, we can use the xGA stat which measures the probability of a team conceding goals (same idea as xG). In this case, a negative gap is better as it indicates that a team conceded less goals than the expected number. In the plot below, we get the last look at Europe’s finest, this time with a defensive focus.
In this case, the Reds lead the way – xGA is the second lowest and actual goals against is the same as Man. City – the lowest number of all those teams. The 8.2 difference indicates a high level defensive ability to prevent rivals from scoring. An interesting point in this plot is Real Madrid – the exceptional defensive skills that were on-display in the UCL final are also evident here – Real Madrid was expected to concede 47 goals but in fact conceded only 31 goals (3rd lowest), that is a defense which is 34% better than expected (and also lucky).
A Domestic juggernaut, facing a beast of competition
Liverpool's brilliance in Europe led the team to as close as possible to a title, only to be foiled by a Goalkeeper's lockdown of a game in the UCL final. In domestic competition, Liverpool won 2 titles (EFL and FA cups) despite facing tough competition in what some view as the strongest league in the world.
Success, titles and wins are a function of financial investment. Comparing Liverpool to its main EPL rivals can give us some sense of the sort of playing field the team faces in this context. The table (data from here) lists different bits of information, over the last 4 seasons, of the main title competitors in the Premier league.
Financial data is detailed in the first column that displays the transfer balance of each team (selling minus buying players). High negative values point to a team purchasing expensive (and/or multiple) players.
Other than the first season listed (2018-19) in which Liverpool's expenses were the highest, in most cases, its main rivals have out-spent the reds, sometimes by a substantial amount (see Man. United).
Now, the point is whether high spending helps performance (and titles eventually). To test that, I added the points gained in league play and each team's goals difference (studies show that GD is a strong predictor of high level performance and titles).
In all but one season, Liverpool and Man. City dominate the data. Liverpool's title in 2019/20 came with a huge point lead over 2nd place City (18 points), and a positive transfer balance. We can also see the two "almost title" seasons in which the reds missed the title by a single point and were super tight with City in the GD column.
One of the lessons of this table is that despite facing competitors with almost no spending limits (i.e. City) or teams that are willing to spend very handsomely (Man. United several times, Chelsea in 2020), Liverpool is at the very top in terms of performance.
Final gems of this past season
As a final point in the discussion of 2021/22, I added a screenshot of the premiere league table around the half-way mark (game week 20, late December 2021). This is how the table looked following Liverpool’s 0 - 1 loss to Leicester. At that point, City had a clear lead and was highly favored to win the EPL. FiveThirtyEight.com soccer projections gave City 77% chance to win the EPL title while Liverpool was second with a mere 19% odds.
What happened since then? The numbers paint a picture of amazing run of excellence.
In the premiere league – of the remaining 18 league games, Liverpool won 16 and had 2 draws. The team's goal difference (great predictor of success remember?) has doubled from +34 to +68!!!
Overall in 2022 (the loss to Leicester was the last game of 2021), Liverpool played a total of 35 games (across 5 months and 4 types of competitions) and lost only 2 games – both in the CL (the last one was the finals loss to Real Madrid; for comparison-sake, City played 29 games in 2022, ended with 3 losses and 6 draws). This is an incredible run of success (also remember that both cups wins took place in 2022) which every reds fan must be aware and super-proud of…
Looking further back
If you have read so far, can I interest you in some more? Well, I went further back and collected data on most of Klopp's tenure, trying to put it in a proper perspective.
Again, I'll start with a broader view – success has been gradual and Klopp led Liverpool to 6 different titles over his entire 7-year tenure. One more overarching point is the successful adoption of a Blitzkrieg style that leads to more possessions and quick, offensive game. I explore this progression with data from the last 5 years (unfortunately, advanced metrics are available only from 2017-18).
First, let's talk about possessing the football. Possession data (measured as percentage of passes attempted in a game) demonstrates this gradual improvement. In the plot below, we see the distributions of the possessions metric in all league play over the past 5 years. Comparing 2021/22 to 2017/18, and even 2018/19, the spread of the distribution is smaller suggesting that more data points are 'clustered around' the mean and median values. The dense data points around the value of 65 fit with the average possession in 2021/22 which was about 63 percent. Comparing this value to the first season (2017/18), we see the increase from a value of 60.3 to 63, which was second in the EPL for 2021/22 (Man.City led the EPL with 68.5 average possession).
Another way to explore this data is to calculate the IQR stat. In this case, IQR describes the difference between games with high possession values and games with low possession values. Small IQR points to condense data around the mean and fewer outlier points. The 2021/22 season had the lowest IQR of 10.5, meaning that most games had similar possession values (which was the highest over the full 5-year span). Previous' years IQR values are higher - 12.75 and 13.75 for 2020/21 and 2019/2020, suggesting more variability in this measure.
Earlier in this post, I talked about the dominant metrics of xG and xGA. We can use these measures to track the change in style brought to Merseyside by Klopp. I already mentioned Liverpool's dominance of xG and xGA in 2021/22. Below, I plot the distributions of xG and xGA per game in all EPL matches over the past 5 seasons.
The blue colored ridges (expected goals per game) increase every year and the distribution is skewed towards higher values (higher xG per game). Liverpool's average xG per game in 2021/22 was 2.34 compared to 1.92 in 2017/18, a 20% increase in (expected) offensive performance over time. Also, the plot includes the full season xG in the column to the right. The increase in values every year presents additional evidence for the offensive improvement over time (going from 72.8 to 89.1 represent a 22% jump).
At the same time, the red colored ridges (expected goals against per game – measures of defense capability) are fairly stable – xGA values 2021/22 and 2017/18 are about equal at 0.9. Considering all the data in the figure, we have multiple indicators for the improved offensive performance, and the stability that the defense has shown over time.
Improvement? Ja.. but how about a few more titles?
All the data shown in this section, and the entire blog post, point to a different and improved team –more aggressive, constantly moving the ball, employing an attacking style, and super-fun to watch. Yet, titles, in particular premiere league titles are still hard to come-by as Klopp's squad won only one premiere league title since his arrival (2019/2020).
Why is that? Well, for once, the EPL is tough and super-competitive with powerhouses like Man. City (sad for me to admit, but City is on a scale of its own) as well as Chelsea and Man. United who won titles over the last 8 years and keep spending on great players trying to improve (see table earlier).
To get a sense of where Liverpool struggled and had lost opportunities to win more domestic titles, I calculated the total number of points gained (3 pts per win, 1 per draw) over the last 5 years and plotted the proportion of points gained of the total possible. In this figure, each year is further unpacked to points gained versus what I termed the Top 3 (City, Chelsea and United) and all other clubs.
The orange bars show the proportion of points gained out of the total possible against the top 3 competition in each season. The blue bar does the same for games against all other clubs. Few observations and pointers that may help explain the struggle for more EPL titles. Against most of the league, Liverpool has been pretty dominant and gained on average 80.6% of the possible points across those 5 seasons. At the same time, getting points from the main competition has been less consistent with a mere 50% of points gained on average. For details of specific match results (number of wins, losses, and draws), see the red column to the right.
When Liverpool obtained at least 50% of the possible points against its top rivals, the EPL title was very much in play – in both 2018/19 and 2021/22, the reds lost the title by a single point. In 2019/20, winning four of six games against the top competition was critical in securing the reds’ first title in 30 years. With respect to performance against all other clubs, being able to dominate is also essential to staying in the title race for as long as possible (as both 2018/19 and this past year demonstrate, when Liverpool gained over 89% of the possible points).
One final comment about points gained in my attempt to put it all in perspective – Liverpool hold the top 2 spots in the list of most points gained without winning the title. The team gained 97 points in 2018/19 (first team with 90+ points to not win the title since 1970/71 Leeds), and 92 points in 2021/22. In both seasons, City won the title by a single point. Those 90+ points seasons (along with 99 points gained in 2019/20 - the title season) are at the very top of premiere league performances in the last 2 decades.
Wrapping-up
Finishing this long post (which is much longer than what I expected when I started to collect and analyze the data), I return to the main point that I started with – let's put this season (and Klopp's reign) in the proper perspective.
The 2021/22 season ended with 'only' two domestic cups (why only?!), and it may have seemed less successful since Liverpool lost both the EPL title and the CL in the same week (probably the hardest 6 days of the year). Yet, my data analysis has demonstrated that 2021/22 should be viewed as one of the best all-around seasons by the reds over the past 2/3 decades. Mo Salah (who finished number 1 in goals and assists) may end it with the World Footballer of the year award – this is just one more point in-favor of this year.
The competition in England is super-tough, and it will only get more challenging with the investments made by the top clubs. But, with a young squad – average age is 26, less than City’s 27, Chelsea’s 26.3 and Man. United at 26.5 - and the extension signed by the boss (happy tears), all reds fans should be excited about the future of this team. The prospect of more titles and, at least for me (and one more best friend) - the fact that Liverpool is always in contention is what we have been clamoring for so long.
Go Reds!
As always, data and code for the analysis in this post are available on my Github.