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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.

AEK Athens beats Greek league leader Olympiakos 1-0

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ATHENS, Greece (AP) AEK Athens defeated Greek league leader Olympiakos 1-0 in an ill-tempered game on Sunday that saw 12 yellow cards and two dismissals.

[ MORE: Messi brace rescues Barca, Pescara earns second win of season ]

Astrit Ajdarevic scored the only goal in the 34th minute with a free kick that deflected off Olympiakos defender Manuel da Costa.

Olympiakos’ athletic director Francois Modesto was sent to the stands for protesting about the lead-up to AEK’s goal. His team’s central defender Alberto Botia was dismissed after a second yellow card in the 75th for pulling an advancing AEK forward’s jersey.

Despite the defeat, its second of the season, Olympiakos has a 10-point cushion over second-place Panionios, which beat 10-man Iraklis 1-0.

PAOK, a 4-0 winner over Veria, remains in third place, one point ahead of Panathinaikos, which beat Asteras 5-0 on Saturday. AEK is joint fifth with Xanthi.

PSG drops points against Toulouse days after massive UCL win

PARIS, FRANCE - FEBRUARY 14:  Julian Draxler of Paris Saint-Germain looks on during the UEFA Champions League Round of 16 first leg match between Paris Saint-Germain and FC Barcelona at Parc des Princes on February 14, 2017 in Paris, France.  (Photo by Clive Rose/Getty Images)
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Just days after its massive (and somewhat unexpected) beatdown of Barcelona, Paris Saint-Germain failed to close the gap on league leaders Monaco.

[ MORE: Messi brace rescues Barca, Pescara earns second win ]

PSG settled for a 0-0 draw on Sunday at the Parc des Princes against eighth-place Toulouse, leaving the Parisian side three points behind Monaco through 26 rounds of action.

[ MORE: Bielsa returns to Ligue 1 with Lille ]

Despite holding the visitors to just three shots (one on target), Toulouse managed to contain a rampant PSG attack, which posted four goals midweek in their rout of the Blaugrana.

PSG’s first strong chance came in the 14th minute when Lucas Moura’s effort was saved in the bottom corner by goalkeeper Alban Lafont.

Meanwhile, Edinson Cavani may have had the game’s best opportunity to break the deadlock when the Uruguayan attacker struck the post from inside the penalty area.

Unai Emery’s group will be back in action on Feb. 26 when PSG travels to Dimitri Payet and Marseille.

Wenger worried over Sutton’s pitch heading Monday’s clash

SUTTON, GREATER LONDON - FEBRUARY 16:  Pundits Paul Merson (4L) and Matt Le Tissier (2L) take part in a training session alongside Paul Doswell manager of Sutton United (L) and players during a Sutton United FA Cup media day on February 16, 2017 at the Borough Sports Ground in Sutton, Greater London. Sutton United are due to face Arsenal in the Emirates FA Cup Fifth round on 20 February.  (Photo by Ian Walton/Getty Images)
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The story of Monday’s encounter between Arsenal and fifth-division Sutton United will be whether the minnows can overcome the mighty Gunners.

[ MORE: Mourinho pleased with United’s “attitude” against Blackburn ]

However, Arsene Wenger already fears a bigger challenge within the game, one that concerns his players’ safety.

Sutton’s 5,000-seat Gander Green Lane features an artificial surface, which is largely uncommon for English and most European venues regardless of club standing.

“First of all the pitch. Secondly their enthusiasm. Thirdly that we are not ready mentally for a big fight and think subconsciously that it doesn’t matter,” Wenger said ahead of Monday’s FA Cup meeting in South London.

In preparation for their meeting with the U’s, Wenger had his side train on their own indoor artificial field on Friday.

“Look, ideally we would like to play on a normal pitch. Competition is as well to deal with what you face, and we’ll face an unusual pitch and we’ll have to deal with it,” he said.

“We practice inside [on Friday] because we have an artificial pitch. It’s not the same as it’s a dry pitch, and at Sutton I’ve heard that’s a wet pitch, they water it before the game. So it will be much quicker than what we have.”

Leipzig beats ‘Gladbach 2-1, cuts Bayern’s Bundesliga lead

Leipzig's scorer Willi Orban, center, and his teammates celebrate their side's 2nd goal during the German Bundesliga soccer match between RB Leipzig and Hertha BSC Berlin in Leipzig, Germany, Saturday, Dec. 17, 2016. (AP Photo/Michael Sohn)
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BERLIN (AP) Leipzig held on for a 2-1 win at Borussia Moenchengladbach to cut Bayern Munich’s lead in the Bundesliga to five points on Sunday.

[ MORE: Messi rescues Barca, Pescara wins second Serie A match ]

Emil Forsberg scored one and set up another for the promoted side to end its two-game losing streak and stay on course for Champions League qualification with its 14th win of the season.

[ MORE: Bielsa makes Ligue 1 return, joins Lille as new manager ]

`Gladbach `keeper Yann Sommer pulled off a brilliant fingertip save to deny Marcel Sabitzer early on, but he was powerless to stop Forsberg from breaking the deadlock after half an hour played.

Sabitzer and Timo Werner played their way through the static `Gladbach defense and Werner laid the ball off for the Sweden midfielder to fire inside the bottom left corner.

The home side was given a lifeline when Marvin Compper brought down Lars Stindl and referee Felix Zwayer pointed to the spot, but Peter Gulacsi saved Thorgan Hazard‘s penalty before the break.

More poor defending allowed Werner grab the second 10 minutes after the break, firing inside the far post after Forsberg played him through.

Jannik Vestergaard pulled one back with a powerful header from a corner to set up an exciting finale. However, six minutes of injury time were not enough for an equalizer.

Leipzig had kicked off to a chorus of whistles from the home fans, who then mostly stayed silent till the 19th minute in protest against the visiting side. Huge banners in the north stand said “Traditional club since 1900” – an apparent protest against Leipzig, founded in 2009 when Austrian energy-drink billionaire Dietrich Mateschitz rebranded a fifth-tier team with his company’s livery before financing its steady promotion through the lower leagues.

COLOGNE 1, SCHALKE 1

Cologne stopped Schalke’s progress but the point was enough for the visiting side to overtake `Gladbach on goal difference in 10th.

Alessandro Schoepf got the visitors off to a flying start in the second minute with the help of the left post, and Leon Goretzka hit the post after half an hour with the home side still struggling to get into the game.

But Anthony Modeste equalized before the break with a fine strike inside the far post, and might even have scored again just minutes later, when his hesitation allowed Benedikt Hoewedes get back and clear.

Guido Burgstaller came closest to a winner for Schalke in the second half, his shot just wide of the far post after beating the goalkeeper.