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Chelsea and Defence in the Premier League: A statistical analysis

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Chelsea FC v FC Barcelona - UEFA Champions League Round of 16: First Leg Photo by Mike Hewitt/Getty Images

Even though football is not a game of massive scorelines, unlike its close relatives such as rugby or gridiron football, the focus historically has almost always been on offence. Even players who were defensive pinnacles of classical teams — e.g. Chelsea legend Claude Makélélé in his time at Real Madrid’s Galacticos — are only given praise when they are doing things beyond their task. Never mind the solitude they give — or not! — week in and out for their teams to go forward and win matches.

Since much of a defence’s influence comes from their off the ball work rather than actual direct interventions, so it is unfortunate that the focus in the still young area of football analytics remains on what players do with the ball. As such, the limelight is turned once again to attackers, midfielders and other players who can rack up stats, while a master at positioning such as Milan’s great Paolo Maldini could very well go amiss with regards to his contribution to his team’s defence when looking only at the numbers taken from the game.

But since the world is not perfect, we try to make the best with what is available to us. And this is what this topic tries to bring. Many of simongabriel’s excellent posts at these corners have had focus on the offensive side of things, and here I will try to bring a view on the other side of the pitch.

At first, my intention is to take a look at how Premier League do as a collective unit in terms of shooting and conversion, since the system is most times what makes or breaks a defender in a team. There is also a minor overview on some defensive stats, as well as goalkeepers and shot-stopping skills, which should develop into something with more detail later on.

Thus, let us move onto the numbers!

(NB: The shooting and conversion numbers were all taken from Scott WillisTableau page. You can see his xG model here. Said data covers the Premier League from its start until February 23rd — which is why Chelsea are still in fourth (oh, those good times...).


PREMIER LEAGUE DEFENSIVE SHOOTING STATS

When looking at the whole league and its collective shooting stats at defences, there are a few things that jump to the eye.

  • Burnley are rather... weird;
  • Stoke City are rather... bad;
  • The top six are (mostly) the top six in every category.

However, aside from Burnley there are not many surprises here. The big clubs are the ones most effective in allowing less goals in absolute numbers, as well as in containing teams from creating big chances (unless you are Arsenal) and headed shots (which are not as valuable as footed ones, but in a league where crosses are the main creative outlet of many teams...).

As previously mentioned, Burnley are the major outliers in the mid-table and no wonder they currently stand at 7th place in the league table. They allow the highest number of shots against their goal at 15.85 per game, but many of those are shots outside of the box at 7.23 on average every match. And they are also standouts in expected goals against the target and goals suffered, where they rank even above some of the PL’s best six teams.

Whereas in other areas, mid to low-ranged teams in the PL table are amidst the mid to lower values of the shooting statistics. The biggest draws are Stoke City, who manage to the worse team in the league in 6 of 10 categories listed; and the gap in many of these statistics between the top six and the teams below them.

The comparisons above help illustrate this massive gap in defensive quality between teams. In every category but the percentage of shots which hit the target against the volume of attempts, the top six teams eclipse the ones below them. And much of that is thanks to Chelsea.

But how does Chelsea compare to its peers at the heights of the Premier League table?

PREMIER LEAGUE’S BIG 6 DEFENSIVE SHOOTING STATS

Another round of things that can be gathered by looking at the data.

  • Some claim that Pep Guardiola’s philosophy of tiki-taka is first and foremost a defensive tactic. No wonder they are the brightest of greens on (almost) everything on the table;
  • For all the talks on how José Mourinho is a “defensive mastermind”, his defence is not good. Not at all;
  • Still, Arsenal manage to be worse than United and the rest of the top six. Basically the Stoke City of the top shelf in England.

The only thing that keeps United from crumbling in defence is their goalkeeper David de Gea. Something that we will explore later.

As for Chelsea, we are very good in comparison not only to the rest of the league as shown previously, but also when going against our direct rivals. Although City are (unsurprisingly) kings in 9 of 10 categories, we often rank in 2nd or 3rd in many of those.

But most importantly, Chelsea are great at stopping teams from creating big chances against them — 0.93 per match — and thus keeping a low number of expected goals from shots on target at 0.69 per game.

Going head to head with the big six, we are above their average in every aspect listed but points (¯\_(ツ)_/¯), total shots, shots within the box and shots outside of it. Still, we are head and shoulders above our opponents in preventing big chances (+26.58%) and in expected goals with shots on target produced against us (+21.05%).


However, to paint a fuller picture we need also to look at how effective the Premier League teams are in converting their shots into goals.

PREMIER LEAGUE CONVERSION NUMBERS

First of all, bullet points!

  • At last, something in which City are not dominating every single thing on the board. Hallelujah;
  • This times around, Chelsea have the greener pastures;
  • Meanwhile, the mid to lower teams at the table are a mess... and so are Liverpool.

If we recall the numbers shown above, in the top six Liverpool are the team with some of the worse defensive shooting stats in the group. Those are only worsened by the quality of their goalkeepers since neither Simon Mignolet nor Loris Karius — although the latter seems marginally better than the former — are dealing well with stopping shots on goal. As per the numbers, more than one in three shots on target versus the Reds are converted, putting them in 19th place in the shots conversion percentage at 13.7%. Only Huddersfield are worse than them!

And they thought the problems were the centre-backs... Though one can say Virgil van Dijk’s purchase was just Liverpool filling their yearly quota of Southampton pouncing.

Near the bottom half of the table alongside Liverpool in the on target conversion department are Arsenal. It is an unfortunate but still expected decline for Chelsea legend Petr Cech, who has certainly had a bigger workload since moving from South-West to North London.

Meanwhile, Manchester United reign supreme thanks to De Gea, with Burnley and Swansea right below them. Chelsea are also in the mix, since Courtois is far from a slouch when it comes to shot-stopping.

Chelsea may still be lacking in their offence when it comes to shots, but their defence knows very well how to deal with them. In 25 big chances allowed in 27 matches, only 32% of those were converted. Only Newcastle, who allowed 48 of those opportunities, and Burnley with 39 were better than us.

On the comparisons between Chelsea and the rest of the league, the Blues reign supreme. There are some categories such as expected goals per shot and percentage of shots on target in which the big six teams perform worse than the minnows. But Chelsea do not follow this pattern, instead eclipsing those averages and most of the advantages their direct rivals have over the Premier League’s lesser sides.

SHOT STOPPING

Things of note here.

  • United do not deserve, but can still afford David de Gea;
  • If Burnley’s Sean Dyche is a Budget José Mourinho, Nick Pope is a Budget De Gea;
  • Why is Joe Hart still a goalkeeper for the English national team?

As the table above shows, Manchester United and Liverpool are the outliers in the top six group, and for totally different reasons. The Mancunians are the best team in goals suffered minus expected goals, at -14. Meanwhile the Liverpudlians lie in 14th place in this aspect, with +5.13.

However, the rest of the top six teams are a tight knit group. From 6th to 9th, you have in order Chelsea (+0.44), Arsenal (+1.08), Manchester City (+1.50) and Tottenham (+1.79) in the ranking.

Yet again, the averages weigh to the side of the big six clubs. Though this is much due to De Gea taking things up several notches with his out-worldly skills at shot-stopping.

Lucky, lucky Mourinho!

PREMIER LEAGUE DEFENSIVE STATS

Defensive actions per game; Source: Whoscored.com

As said at the beginning of this piece, defenders and their contributions can always go amiss if you only look at the actions they do on the ball. And the data above does a good job in proving that point.

In fact, the top six teams perform BELOW their mid to low table competitors in many of the categories listed. Which goes to show that looking at things such as numbers of tackles made, interceptions, clearances and so forth when looking into defenders is not the proper way of meddling with defensive data to draw definitive conclusions. They can certainly help, but they will not paint you a big picture.

CONCLUSIONS

To evoque the often wise words and terms of @CFCgwlb, Mourinho truly is a Chequebook Pulis. Unlike Conte, the Portuguese does not make due on his fame by mounting a solid defensive unit, instead having to rely heavily on De Gea’s services to keep things tight at the back while also being a tad lacklustre when it comes to scoring goals.

And all of this exercise helps prove simongabriel’s point on how Chelsea are being let down by their attack and their bad aim at target. The title defence this season would still be a hard task since City have been pretty great not only in attack but also in the defensive side of things, even though this comes from all of their work on retaining the ball. Still, the Blues could be sitting comfortably in the top four zone instead of gasping for air — and a Champions League berth — as the season draws to an end.

Maybe in this final stretch of the season, our attack will find a way to catch up with defence and we will be all laughing over our worries of finishing outside the top four in the forthcoming years. Starting with Crystal Palace, this is all what we are hoping for!


Next up will be a comparison with Courtois against their peers in some key aspects of goalkeeping duties. And most importantly, we shall look at who we could bring in case he decides to take his services to Madrid...

See you!