written by – Rangers Report photo courtesy of – Getty Images
My ultimate goal in this project was to develop a defensive rating system for center backs. A rating system that could be used as an entry point to evaluate defensive play, recruit players & even identify trends in opponents.
The rating would combine shot suppression with how often defenders were actually doing stuff (passes in the defensive third, tackles, interceptions, & clearances…you know – defensive stuff).
I leaked out results via Twitter as I finished tracking different teams.
I was excited by the results.
Ahhh…the stat formerly known as the DPSS (Defensive Possession & Shot Suppression) Rating.
I was all ready to go….but first I wanted to set the stage by using the data collected to determine if having a left-footed center back, paired with a right footed center back was an overrated phenomenon or an actual priority managers should seek out.
That was Part One. The results proved that there was no real reason to go out of your way to pair a lefty with a righty & that when two right-footed center backs were paired together – the results were basically identical to a ‘balanced’ pair of center-halfs.
But….my plan was flipped upside down by the following facts: in the 2016-17 season, 56% of shots, 55% of scoring chances (more on that later), & 62% of the goals came from shots taken on the right side of the pitch against the left side of the defense.
I was expecting closer to a 50/50 split, but 56% of the shots coming from the right meant that only 44% were coming from the left (pretty fancy math, huh).
This kind of blew my mind…(I know, I know… ‘get a life’….whatever)…..but ultimately, I was looking at three months of work going down the drain. How can I justify using a rating to assess center backs when one side of the pitch sees 12% more of the shots?
Then the sleepless nights started….
Playing as a left sided center back was a more difficult job then playing on the right. You’re more likely to have shots taken from your zone of influence & way more likely to concede goals from your side of the pitch.
Thankfully, with the support of Matt Cane & Ryan Stimson, via some frantic emails (mostly frantic on my end), I was able to revise my plan of how I was going to use this data & apply it to a defensive rating system. The work of Cane & Stimson have been huge influences on this process & in particular, this post from Cane’s blog Puck++ is what kickstarted this project.
Before we get to the findings, let’s quickly review the process (first introduced in part one).
SPOILER: Before I lose you….the five highest rated defensive center backs in the EPL last season were:
Arsenal’s Shkodram Mustafi
Burnely’s Michael Keane (who just signed with Everton for £30 million),
Everton’s Ramiro Funes Mori (when healthy)
Phil Jones (Manchester United)
Steve Cook of Bournemouth.
Some surprises there? Phil Jones, really?
Let’s see how the stats played out…
To get a sense of shot suppression, we need to know where the shots are coming from. So I tracked the shot data from each EPL match from the 2016-17 season.
I split the pitch in half & recorded which half of the pitch the shot came from. I only included shots that started within the frame. Notice the blue shot (a shot that was on target) & the yellow shot (a goal) originated from outside this frame & were not counted. Shots from that far out were less likely to be impacted by a center back. Make sense?
So in this example, there were two shots counted & both came from the attacking right side. Given that this is the point of view of the attacking player, realize that those two shots came under the zone of influence of the left-sided center back (see it is harder to play on the left side).
As the data adds up you can see what percentage of shots came from either side of the pitch. Like I mentioned in the previous post, this isn’t perfect. Football is a fluid sport. Sometimes a left sided center back is caught up on the other side supporting his partner. Often a breakdown occurs elsewhere that the center back has no control over.
But, over hundreds & thousands of minutes some definitive trends occur…these trends should be learned from & can bring some real insight to the effectiveness of the different center backs in the league.
Now, for the twist….remember one center back has a more difficult task then his partner.
Take Liverpool’s Ragnar Klavan as an example. Klavan is a left-footed center back who played nearly 1,500 minutes as a left-sided center back. When he was on the pitch, 56% of the shots against came from his side, meaning 44% of the shots came on his partner’s side.
In my original rating system, this hurt Klavan. He was not suppressing shots as well as his partner & as a result the majority of scoring chances & goals were also coming from his defensive zone of influence.
But remember, I tracked over 9,000 shots & the data showed that 56% of shots came from the right side (against left sided defenders). Couldn’t you argue that Klavan was performing as expected relative to other center backs playing on the left side?
This is where finally found my zen moment. Why don’t I just show a defender’s shot suppression stats relative to the rest of the league. This has become very common in the hockey analytics world, as players’ stats are evaluated in relation to other players (usually their teammates).
Back to Klavan. His Relative Shot Suppression Rate (RelSS%) is 0.00. His 56% is no different than the rest left-sided center backs in the EPL.
Another example is Sunderland’s left sided center back Papy Djilobodji. Before my moment of clarity, I was pretty blown away by how bad Djilobodji was at suppressing shots. When he was on the pitch, 63% of shots came on his side & only 37% on his partner’s side.
I bring up the partner’s rate because remember my ultimate goal was to create a defensive rating. Because I ultimately want to combine two positive numbers, I used the percentage from the partner’s side. If a player never allowed a shot on his side of the pitch – what the hell would you gain by starting with 0% as a number…100% would be a better number to work with.
Back to Djilobodji (thank you copy & paste) — 37% of the shots came on his partner’s side & the league rate for a left sided center back would be 44% of the shots coming on the opposite side.
So…Djilobodji’s RelSS% is -0.07 (0.37 minus 0.44). That’s still pretty bad…actually it’s among the worst rates in the league last season.
The best, you ask???
I used 1,000 minutes played as the minimum here to avoid the shock of seeing Daniel Ayala or Nathan Ake in the top 10…that’ll come in a few minutes.
When it comes to shot suppression, you see that there’s Nicolas Otamendi & Virgil van Dijk & then everyone else.
Otamendi basically split his time playing on the left & right last season. When on the left, his RelSS% was 0.04…which is very good. When he was on the right, his RelSS% was 0.18 – which is off the charts good. As a right center back, 74% of the shots came on his partner’s side – when you subtract the league average of 56% from that you get Otamendi’s Relative Shot Suppression Rate of 0.18.
Van Dijk spent 95% of his minutes as a left center back for Southampton & the majority (54%) of the shots came on his partner’s side…normally that rate is flipped…which explains why he is so in demand during this transfer season.
Now, remember my original goal was to create a defensive rating for center backs. This is merely an attempt at measuring defensive impact by combining the player’s RelSS% with the aforementioned defensive stuff they do: completed passes in the defensive third, clearances, interceptions, & tackles won. I combined those defensive possessions (much better term then stuff) & averaged them out on a per 90 minutes basis & multiplied that rate with the RelSS%.
Below are the top 25 center backs based on that defensive rating, this time with a minimum of 700 minutes played.
*Note that the RelSS% was rounded up for your sanity & that’s why someone like Gareth McAuley’s rating doesn’t look like it matches up. His actual RelSS% is 0.0148709.
Remember my spoiler from earlier about Mustafi & Keane being the top rated defensive center backs last season? Where are they on this list? Mustafi is 22nd, while Keane is 58th!
Rating center backs on shot suppression is one thing, but we all know that not all shots are created equal. To me, one of the qualities of a good center back is, if they are going to allow a shot, to force that shot to the outside into a less dangerous area.
Basically, can they limit the amount of scoring chances that come from the shots they do allow on their side of the pitch.
Scoring chances are any kicked shots from inside that red, shaded area & also are headers that come from within the vicinity of the six yard box. All other shots have been ‘forced outside’ of the danger area & are not considered scoring chances given the low scoring rate of those shots.
Below you’ll find the top Relative Scoring Chance Suppression Rates (RelSCS%) from last season’s center backs. It’s the same concept as the shot suppression rate…the only differences are that only scoring chances are considered & the league rates are 55% of scoring chances come from the right & 45% from the left (from the point of view of the attacking team).
Again, being a left-sided defender is more difficult than being deployed on the right.
1,000 minute limit
There didn’t seem to be much love for Mustafi’s first season with Arsenal but the fact is that opposing teams really struggled to create quality scoring chances on his half of the pitch.
In his nearly 2,200 minutes, Mustafi only allowed eleven scoring chances from his side of the pitch. There were 28 scoring chances coming from his partner’s side. That equates to 72% of the scoring chances coming from his partner’s side – the league average for players on the left (where Mustafi’s partners played) was 55%…that translates to a RelSCSS% of 0.17.
Keane played over 3,000 minutes for Burnley & had similar rates. Keane saw 22 scoring chances from his side of the pitch, while his partner allowed 53. Even though Keane allowed twice the amount of scoring chances, he still only allowed 29% of them to come from his side of the pitch. Keane was under much more pressure than Mustafi, but they both did a much better job than their center back partner.
Here are your top 25 rated center backs, based on their combined Defensive Possessions per 90 with their RelSCSS%. The minimum is 700 minutes played.
Remember numbers are rounded up. For example, Luiz’ RelSC% is 0.0251449, while Delany’s is 0.0272891. That’s how they end up with the same rating.
- Denayer played limited minutes, but when he was on the pitch only 40% of the scoring chances were on his side. Given that he played 81% of his minutes on loan from Manchester City as a left-sided center back – his job was harder. That is why his RelSCS% is so high.
- You’ll notice that some players are ‘rated’ higher than some even if their RelSCS% isn’t higher. For example, Phil Jones is rated slightly higher than Steve Cook despite a lower RelSCS%. The difference is that Jones averaged 26.57 defensive possessions per 90, while Cook averaged 23.58. Jones had a little more defensive stuff to do in order to limit the chances coming from his side.
Is this a definitive list of the best center backs? No…but it’s a conversation starter based on facts.
The stats aren’t perfect, but they are entry points to further analysis. When I did a poll of who were the best center backs in the EPL, only 28% of the 195 ballots said that Mustafi was among the top 10. Only 24% had Otamendi in the top 10 & Phil Jones only was on 7% of the ballots.
There was a significant push for Laurent Koscielny to be included. He’s a player I’ve always regarded highly as a defender. Most observers have.
His Relative Shot Suppression Rate? -0.01.
His RelSCS%? -0.10.
Only five center backs who played more than 1,000 minutes had a lower RelSCS%. When Koscielny was on the pitch for Arsenal, 63% of the scoring chances came on his side. Even though he played the majority of his minutes on the left side, which is a more difficult task….remember that RelSCS% takes that into account. You can either dig for excuses….or ask yourself why? Why are teams having success exploiting Koscielny’s side of the pitch?
Let’s stop for now….there’s a part three & maybe even a part four coming up. Next up: we’ll share the results from each team. That way we can see who are each team’s best (& worst) defenders & who deserves more (or less) playing time).
Here’s a couple of samples:
All of the data from this study will be released once all the posts have been written.