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.

WATCH: Liverpool battering Bournemouth with highlight reel half

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Philippe Coutinho is capable of elite magic, and he conjured up some fantasy on Sunday at the Vitality Stadium.

[ MORE: Watch via NBCSports.com ]

Liverpool and Bournemouth were scoreless when the Brazilian dribbled past Simon Francis and Lewis Cook on a mazy run, taking Andrew Robertson‘s square pass and dancing through daylight.

If only there were a body cam on Adam Smith, who was chasing Coutinho the whole time!

Dejan Lovren — does this require we say “of all people?” — then scored a diving header after Roberto Firmino saved a wayward corner kick.

And Mohamed Salah, what else can you say about the 20-goal scorer (in all competitions)?

Salah would get his goal in stunning fashion, bodying off a defender before dribbling past two more to finish with an off-balance belt past Begovic.

Kaka calls it a career; Won World Cup, Ballon d’Or

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He’s the last Ballon d’Or winner neither named Messi nor Ronaldo, and he’s calling it a career.

Kaka announced his retirement on Sunday after a gleaming career on three continents.

Born Ricardo Izecson dos Santos Leite, Kaka won the 2002 World Cup with Brazil and also boasts two Confederations Cup wins amongst his 92 caps and 29 international goals.

[ MAN CITY-SPURS: 3 things |  Studs and duds ]

Kaka debuted for Sao Paolo in 2001, and left for AC Milan three seasons later. Thrice names in the UEFA Team of the Year and twice the Serie A Footballer of the Year, Kaka won Serie A with Milan and La Liga with Real Madrid.

He spent the final three seasons of his career in Major League Soccer with Orlando City SC, and was magnificent. The 35-year-old scored 25 goals with 19 assists for the Lions.

West Brom 1-2 Manchester United: Red Devils hang on

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  • United back into second
  • Lukaku scores 10th PL goal of season
  • Baggies winless in 16

Romelu Lukaku and Jesse Lingard scored first half goals and Manchester United held on to beat West Bromwich Albion 2-1 at the Hawthorns on Sunday.

Gareth Barry scored the Baggies’ lone goal, as Alan Pardew‘s men sit 19th and without a win since August.

United pulls three points ahead of Chelsea, and is 11 points back of Man City.

[ MORE: Watch full PL match replays ]

West Brom wasn’t intimidated by the task at hand, and James McClean was particularly lively as the Baggies tried to find an opener.

But United quickly settled into control through possession, albeit without any effective incisiveness.

That changed when Lukaku rose to deposit a trademark header beyond the reach of Ben Foster, converting Marcus Rashford‘s cross with power.

After a moment of danger provided by Allan Nyom and Salomon Rondon, United made it 2-0 when Lingard took a lay-off from Juan Mata and hit a shot that Ahmed Hegazi deflected past Foster.

Jake Livermore forced David De Gea into a low save in the 44th minute.

 

[ MORE: Latest Premier League standings ]

[ MORE: Full lineups, stats, box score ]

The Baggies pulled one back as both Evans and Barry could’ve tapped in a loose ball off a corner kick.

Barry did, and United was on its heels. Credit Alan Pardew for his substitutes of Barry, Chris Brunt, and Jay Rodriguez (though they were, after all, on the bench).

Rodriguez powered a header off Brunt’s cross wide of the near post with about five minutes to play.

And a scramble in front nearly put the Baggies level, but De Gea was there. The keeper was kicked by Ahmed Hegazi and came up smarting.

WATCH LIVE: Bournemouth vs. Liverpool

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Liverpool looks to pile misery on Bournemouth while increasing its Top Four stock with a visit to the Vitality Stadium on Sunday (Watch live at 11:30 a.m. ET on NBCSN and online via NBCSports.com).

WATCH LIVE, ONLINE, HERE

The Reds can climb back into the Top Four with a win, and will do so with Sadio Mane, Danny Ings, and Dominic Solanke amongst their bench players.

Bournemouth starts Jermain Defoe, Joshua King, and Jordon Ibe amongst its attackers.

LINEUPS

Bournemouth: Begovic; Daniels, Ake, Francis, Smith, Pugh, Surman, King, L. Cook, Ibe, Defoe. Subs: Boruc, S. Cook, Gosling, Arter, Fraser, Stanislas, Afobe.

Liverpool: Mignolet, Gomez, Lovren, Klavan, Robertson, Henderson, Wijnaldum, Oxlade-Chamberlain, Coutinho, Salah, Firmino. Subs: Karius, Milner, Mane, Lallana, Ings, Solanke, Alexander-Arnold.