What can we learn from defensive statistics?

Date published: Saturday 7th January 2017 11:18

Individual defensive stats are among the trickiest to interpret. For one thing, they depend heavily on a team’s style of play. If you play passively, you’ll have a lot of blocked shots and clearances. If you press, you’ll have relatively few interceptions, because you’ll often win the ball before passes are made, and/or opponents may try lots of long aerial balls to beat the press. And across the board, the more possession you have, the fewer quantifiable defensive actions you can perform. Football statisticians will almost always adjust for possession when using defensive stats.

But the bigger problem with individual defensive stats is they don’t always measure performance. This is clearest when we come to players in the back line. Tackles, interceptions, clearances and blocks tell us many things, but they generally don’t tell us how well defenders mark, or how often they make the right decisions. We simply don’t have stats that tell us how much space an attacker is given, or how often and in what ways a defender is beaten. A centre-half can have 15 clearances in a match, but also let a striker through twice to score. Another centre-half may have zero tackles, zero interceptions, and relatively few clearances, but mark so well that no one gets through.

So this will be the first of two articles discussing individual defensive stats and how they might reflect competence and style. But caveat emptor really comes into play here.

(By the way, I forgot to mention earlier that I’m mostly using Whoscored.com stats in this series. That’s because I don’t have access to the complete Opta stats. They differ most prominently in counting tackles, but it’s the principles that count most here)

 

Tackles
For stats purposes, a tackle is when you dispossess an opponent with a challenge for a ball that’s on the ground. The tackler doesn’t have to go to ground himself. Among players with at least 1000 minutes this season, the top ten in tackles per 90 minutes are Idrissa Guèye at 5.0, followed by Jordan Henderson, Francis Coquelin, Daniel Drinkwater, Oriel Romeu, Granit Xhaka, George Friend, Pedro Obiang, Joe Allen and Danny Rose. You’ll notice that eight of these are central midfielders and two are fullbacks. These are the positions with the most opportunities for tackles: DMs because so much of the play runs through the middle, and FBs because they have players running at them.

The three that stand out to me here are Drinkwater, Allen and Rose.

Drinkwater, like N’Golo Kanté for Chelsea, plays in a two-man deepish central midfield, but it doesn’t seem to have affected his numbers. In fact, his tackles/90 are up from 3 last year to 3.7 this year, reflecting Kanté’s absence. Allen generally plays in a more advanced position than DM, so his figures are that much more impressive. Rose plays for a team that has a fair amount of possession, which makes his ranking particularly outstanding. A further look shows that Rose has jumped from 2.8 tackles/90 last year to 3.2 this year.

For DMs and FBs, tackle stats to some degree must reflect quality of performance. The names on this list – and remember that Kanté led the league last year – are ones we’d expect to find. Guèye and Romeu were in the top five last year as well. But tactics must also play a part. Victor Wanyama isn’t on this list, and in fact ranks quite low at 2.5, about the same as Andros Townsend. He sits deep for a Spurs side that has a strong central bias, which tries to funnel opposing attacks toward the flanks. When he played for Southampton, his numbers in successive seasons were 3.5, 3.5, 3.4. Claudio Yacob, a tackler if there ever was one, has seen his numbers drop from 5 to 3.4 to 3.0 with Tony Pulis in charge, as he plays in a midfield that sometimes seems all defenders. And we’ve already talked about how Kanté now splits duties with Matic.

But if with DMs and FBs we can make careful performance evaluations based on tackling stats, central defenders are another matter. Tackling is the natural job of a holding midfielder or a full-back, but not so much of a centre-half. In fact, tackling stats for central defenders are much more useful in measuring style than competence.

An example: the current tackles/90 leader among central defenders is Nicolas Otamendi, at 2.7 (discounting Cesar Azpilicueta as he started the season as a conventional full-back). This is quite remarkable, considering how much Manchester City have the ball. But watch Otamendi, and you’ll see he’s a very aggressive defender, always moving forward to confront his man. (Note also that he usually plays wide in a three-man defence, so he covers a large area.) Second on the list is Jordi Amat, at 2.2. Amat is also an aggressive defender, and his numbers are high for an average possession team like Swansea. But there’s a key difference: Otamendi is a good, if erratic defender; Amat is not a good defender at all.

Now let’s look at Gary Cahill, who like Otamendi mostly plays as part of a three-man defence. Chelsea have less possession than Man City, but his tackles/90 are significantly lower, at 1.4. He’s just not as aggressive as Otamendi. A player nearby is Ryan Shawcross at 1.3, who plays for an average-possession Stoke and tends to sit back. But although Cahill may not be the perfect defender, he’s a class above Shawcross.

The central defenders with the lowest tackles/90, from the bottom up, are Michael Keane at 0.7, Michael Dawson, Wes Morgan, Lamine Koné, Ben Gibson, Robert Huth, Scott Dann, Steve Cook, Toby Alderweireld and Damien Delaney. What’s interesting here is that several of these names play for low-possession teams like Burnley and Leicester. But these teams tend to sit deep and let attackers come on to them, so the defending is passive. Notice also that several of these players were high on the shot-blocking list. If you sit back, you’ll block lots of shots and won’t make many tackles.

Often the best use of tackling stats is in individual matches, where we can note particularly remarkable performances both good and bad. A few weeks ago Didier Ndong had five tackles for Sunderland against Watford, which is not only high but outstanding for him, when you consider his average is only 2.1. And remember that brilliant second-half defensive performance by Chelsea against Crystal Palace? Kanté, Matic and Victor Moses each had four tackles in four attempts that day, an impenetrable wall. On the downside, in Bournemouth’s recent game against Chelsea, Dan Gosling, averaging a good 3.1 tackles/90, had zero tackles in six attempts. The counter-attack just ran right by him.

Those last stats remind us that not only can we measure tackles, but also tackling success percentage. Like aerial duel percentage, this is a relatively pure number that can actually tell us a lot about skill. Without going into details – you can check the definitions yourselves – Opta and Whoscored.com differ wildly on their numbers here, but topping the list among regulars this year is Nathaniel Clyne at 86% according to WhoScored stats. By and large, back-line players score higher than holding midfielders at tackling percentage, because the man with the ball generally has less room to manoeuvre. Players very low on this list are usually strikers and attacking types like Dusan Tadic and Riyad Mahrez.  Who’s the top striker in this category? I guessed Troy Deeney, but it’s none other than Jermain Defoe at 75%. It’s the Allardyce/Moyes influence.

 

Interceptions
Interception leaders are generally deep-lying midfielders and central defenders, with full-backs showing up at times as well. The leaders in interceptions/90 last season were Kanté at 4.6, followed by Coquelin, Guèye, Yohan Cabaye, Laurent Koscielny, Yacob, Leon Britton, Nathan Aké, Otamendi and Valon Behrami. For this season so far, it’s Yohan Cabaye at 4.0, followed by Curtis Davies, Ander Herrera, Nacho Monreal, Coquelin, Winston Reid, Papy Djilobodji, Friend, Shkodran Mustafi and Otamendi.

For holding midfielders, interceptions can be a measure of involvement in the game, but as a rule tactics play an even larger part here than with tackles. Tackles will always be a necessity at some point, but interceptions are to a significant degree optional. Even though on average interceptions are less frequent than tackles, team interception totals always show a much wider range than team tackle totals. As José Mourinho famously did for many years, you can choose a passive defensive approach. Or like Arséne Wenger, you can take a more aggressive tack, which in recent years has put Arsenal regularly near the top in this category. So we have to be even more careful reading interception stats than tackle stats.

Let’s take Wanyama again. As we mentioned at the beginning, pressing teams generally make fewer interceptions. His last two years at Southampton were 2.3 and 2.4, but he’s dropped to 1.3 with Spurs. Walter Mazzarri’s Watford side isn’t as active in their own half as Quique Flores’ version last year, and Valon Behrami has seen his totals go from a career-high 3.4 to a career-low 1.5.

As with tackles, interception stats for central defenders are a matter of style. Note that the aggressive Otamendi makes this list for both years, again despite Man City’s high possession numbers. Koscielny is usually high in the interception rankings as well. But Koscielny doesn’t make the tackling lists, and his interceptions seem less a function of aggression than precision. For a great demonstration of style differences, compare Koscielny with Per Mertesacker, his partner for several years at Arsenal. In 2013-14, Koscielny led Mertesacker in interceptions 2.9 to 1.7. In 2014-15, it was 3.7 to 2.1. In 2015-16, an even greater spread, 4.0 to 1.6. It’s clear that their styles have diverged with the years.

But remember that tactics play a larger role with interceptions than with tackles. Let’s look at the central defenders lowest in interceptions/90, from the bottom up: Ryan Shawcross at a very low 1.0, followed by Alderweireld, Francis, Dawson, Vertonghen, Phil Jagielka, Huth, Cahill, Gibson and Delaney. Shawcross at the bottom is intriguing, and checking his history, we find he’s at an all-time low. But then so are Glenn Whelan and Erik Pieters, other Stoke City veterans. So it’s no surprise to find Stoke with its lowest team interception total since Mark Hughes took charge. The pairing of Vertonghen and Alderweireld is also suggestive, and in fact both have dropped significantly since last year, which must reflect a tactical decision by Mauricio Pochettino. One more note on this list: Michael Dawson, our leader in blocks, is very low in interceptions. He sits tight and stops everything that comes his way. Incidentally, one John Terry, a very similar player, would have been rock bottom on this list if he’d played enough minutes.

Again as with tackles, interception stats can be useful at individual game level. When Arsenal defeated an attack-minded Bournemouth at home, Koscielny and Mustafi registered an outstanding five interceptions apiece. And when that same Bournemouth threw everything they had at Stoke’s left side, Erik Pieters, averaging only 1.6 interceptions/90, delivered a whopping six (and eight tackles, too).

Nearly 2,000 words and we’re not done, which shows you how complex individual defensive stats can be. Next time we’ll look at a few more numbers, and try to draw some overall conclusions.

Peter Goldstein

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