Compromised numbers: Why the statistic you see may not be actual possession

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One of the amazing statistics to come out of last Wednesday’s UEFA Champions League match was the possession number. Barcelona was reported by UEFA was having held the ball 72 percent of the time, an amazing figure against a club of Chelsea’s caliber. For those who have tried to find significance to correlations between possession and victories, the number must have been both remarkable and beguiling. After all, Barcelona lost, giving more credence to the hypothesis’ main qualm: What if one team doesn’t care about holding the ball?

The next day, the possession story got even more confusing. Supreme stat overlords Opta reported that Chelsea had only managed 20 percent of the ball. What? Even less time in possession? How freakish is this data point going to get?

That, however, is not the story. At least, it’s the story in light of what Graham MacAree notes at Chelsea fan site We Ain’t Got No History. As he’s found out, Opta seems to be miscalculating possession; or, better put, Opta is not reporting a number consistent with the normal expectation for a possession stat.

The normal expectation: When one team has the ball, they’re in possession. I think we can all agree on this, right? This still leaves a lot of gray area. For example, who gets credit for possession when midfield chaos leaves neither side in control? Does one team get possession on a goal kick, when most goal kicks lead to 50-50 midfield challenges? And more broadly, what happens when play is dead but the game clock is running?

I’ve always assumed this is like a chess clock. When one team controls the ball, you hit a button that sends their dials turning. When the other fully regains possession, you hit a button. One clock stops. The other starts running. Those in between moments? They’re governed by one rule: Until possession changes, don’t touch anything.

That, apparently has nothing to do with Opta’s calculations. In fact, Graham’s research suggests Opta doesn’t even run a clock, which may be why they never report possession in terms of time. Instead, the relation between reported possession and total passes suggests Opta just uses passes. As Graham found out, if you take a team’s pass attempts a divide it by the game’s total attempted passes, you have Opta’s possession stat.

What does this mean? Let’s take a totally fake scenario. Barcelona plays three quick passes before trying a through ball that rolls to Petr Cech. It all takes four seconds, while Petr Cech keeps the ball at his feet for eight seconds before picking it up, holding it for five seconds, then putting it out for a throw in, which takes eight more seconds to put back into play.

Despite Barcelona having possession for only four of those 25 fake seconds, they’d have 80 percent of Opta’s possession (three good passes plus one bad, while Chelsea had only Cech’s unsuccessful pass). A logical expectation of a zero-sum possession figure would have that as either 16 percent or (if you credit the time out of play as Barça’s, since they’d have the ensuing throw) 48 percent Barcelona’s. Or, if you do a three-stage model (that’s sometimes reported in Serie A matches), you’d have 16 percent Barcelona, 52 percent Chelsea, and 32 percent limbo/irrelevant.

Of the three methods of reporting possession, Opta’s bares the least resemblance to reality; or, it’s the one that deviates furthest from what we expect from a possession stat.

Ironies being a thing these days, there are two here. First, Opta is the unquestioned leader in soccer data management. How could this happen?

Second, Opta isn’t trying to hide their methods. In fact, they’ve published a post on their site detailing not only their practices but their motivations and research, an investigation that found their approach “came up with exactly the same figures (as time-based methods) on almost every occasion.”

You would think two curmudgeons like Graham and myself would have found this, right? Graham had a reader point it out to him, while a representative from Opta magnanimously pointed me to the piece without the seemingly necessarily indignation of explaining how a Google search works. After all Graham’s work and head scratching – after my lack of work and similar head-scratching – we could have just gone to Opta’s site.

“We try to be as transparent as possible with this stuff,” Opta said when I asked them about it. Certainly, they should be commended being so up front about their methods. After all, they’re a business that makes money off their work. They don’t need to give away their secrets.

But that’s a secondary issue. The main one: Why is a data house like Opta, reputed as the industry standard, taking this short cut? Or, why haven’t they renamed their measure? Granted, the perception that it is a shortcut may have more to do with our expectations than their intent, though based on their defense in the post, it’s clear they do see this as an accurate way of describing possession.

Still, the number they publish is completely redundant to the raw passing numbers also distributed. Why put the measure out at all if not to check a “possession stat” box on a list of deliverables?

Opta’s possession stat shouldn’t be cited in reporting, and if it is, the word “possession” shouldn’t be used to describe it. Reader expectations for anything labeled “possession” are drastically different than what Opta’s producing. The number is confusing to the point of being misleading. It’s becoming counter-information because of its poor packaging.

Even though Opta’s post on the topic is 14 months old, most will be surprised to hear this “news.” It’s disconcerting for anybody who is hoping a SABR-esque revolution’s on the horizon. Almost all of the huge volume of data to which we have access has been useful, but where people are expecting something akin to linear weights to be published tomorrow, we can’t even agree on the terms (let alone the significance of them).

Graham probably puts it better:

I’m completely fine with keeping track of passing volume – I’ve done it before myself. What’s frustrating, from an analyst’s point of view, is that we’re being sold a dud. A statistic that ostensibly measures possession measures something that is not possession, and gets repeated as authoritative anyway.

And people wonder why football statistics don’t get taken very seriously.

Report: Newcastle’s Clark knocked out on Spanish dance floor

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A wild story out of Spain says an Englishman knocked Newcastle United defender Ciaran Clark unconscious at a night club.

[ MORE: Sampaoli defends Messi ]

Clark was on vacation in Spain, where he was spending time at Crystal’s Bar in Punta Ballena, Magaluf very early Sunday morning.

Clark and a man “in his 30s” got into an argument that saw the Irish defender knocked out, according to the BBC.

Clark was left unconscious and taken to hospital after an argument between him and the suspect broke out on the dance floor.

The 28-year-old suffered cuts and bruises to his face.

Clark, 28, scored twice in 20 Premier League appearances this season, his second at St. James’ Park.

WATCH: World Cup, Day 9 — Iceland’s next step, Brazilian bounce back?

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Brazil is one of the favorites of the 2018 World Cup, while Iceland is the smallest nation to qualify for the world’s biggest tournament.

[ MORE: Latest 2018 World Cup news ] 

On Friday, both enter their second match days feeling quite different after 1-1 draws.

They won’t face each other, of course, but the contrast is striking nevertheless.

Brazil opens the day’s action when it squares off with Costa Rica, who fell to Serbia in the opener. For Serbia, a dark horse of the tournament, it will be a meeting with Switzerland.

Then there’s Iceland’s bid to climb into the Group D driver’s seat by knocking off Nigeria. A win from Iceland would make Lionel Messi and Argentina’s task of qualifying for the knockout rounds extremely unlikely.

Below is Friday’s schedule in full.

Click here for live and on demand coverage of the World Cup online and via the NBC Sports App.


2018 World Cup schedule – Wednesday, June 20

Group D
Nigeria vs. Iceland: Volgograd, 11 a.m. ET – LIVE COVERAGE

Group E
Brazil vs. Costa Rica: Saint Petersburg, 8 a.m. ET – LIVE COVERAGE
Serbia vs. Switzerland: Kaliningrad, 2 p.m. ET – LIVE COVERAGE

Sampaoli defends Messi, blasts Argentina

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Jorge Sampaoli is lambasting his team after a 3-0 loss put Argentina on the edge of failing to qualify for the 2018 World Cup’s knockout rounds.

“The reality of the Argentina squad clouds Lionel Messi’s brilliance,” Sampaoli said. “The team doesn’t gel as well as it should.”

[ MORE: Modric urges humility ]

Sampaoli said his players could not find a way to get the ball to Messi, and that the introduction of Boca Juniors youngster Cristian Pavón was aimed at opening up the field a little bit.

And Sampaoli is not shying away from the long-discussed comparison between Messi and Portuguese star Cristiano Ronaldo. From the BBC:

“Cristiano is a great player and he has achieved a lot with club and country. Right now it is hard to compare these two players because of the ability in the Argentinian squad clouds the judgment. Leo is in a difficult position because the squad doesn’t gel with him. As coach I have to accept that. I don’t feel shame but I definitely feel pain. It has been a long time since I have gone through this experience as a coach and obviously it is more painful when I’m wearing the colours of my country.

“We have no alternative but to give it our all in the final match. We have not performed at the level the country expects. We were ambitious ahead of the game but now it is harder for us as a group. We did think this would be the match we can take off as a team, but it wasn’t in the end. I think this is an excellent squad but we didn’t gel or come together. We need to take advantage of the next match, when the pressure will be on, and hope to progress.”

Now, of course Sampaoli is going to defend Messi, but Argentina’s team is not chopped liver. The side certainly isn’t as deep or solid as Croatia, but 1-1 with Iceland preceded this one.

That said, Argentina’s performance once Croatia essentially decided to surround Messi was unacceptable. If favored Nigeria doesn’t handle its business against Iceland, the World Cup finalists won’t have a prayer of going back.

Modric urges humility after big win, stunning goal (video)

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There are few teams who’ve looked as strong as Croatia at the World Cup in Russia.

[ RECAP: Argentina 0-3 Croatia ]

Zlatko Dalic’s men now have a pair of shutout wins against decent competition, topping Nigeria 2-0 over the weekend before hammering Argentina 3-0 on Thursday.

The nature of those performances will have many, us included, debating just how far Croatia can run in this tournament. Veteran midfielder Luka Modric is hoping his team doesn’t do the same.

Let’s not be euphoric or get ahead of ourselves,” Modric said. “Of course this win will boost our confidence for the next game, and we have shown we can create opportunities, but let’s keep our feet firmly on the ground.”

Modric noted that Willy Caballero‘s howler “was a shot in the arm,” but added that they had played a “perfect game.”

That’s true. And while so much focus will be on Messi’s struggles, don’t sleep on the terrific performance of Vatreni. 

Modric also seemed to bristle when asked about shutting down Messi.

“I don’t want to talk about other players. We are happy with our own performance. We wanted to cut out Messi receiving the ball because he is the most dangerous player.”