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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.

Lionel Messi picks up hamstring injury, will travel with Argentina anyways

BARCELONA, SPAIN - AUGUST 20: Lionel Messi of FC Barcelona looks on during the La Liga match between FC Barcelona and Real Betis Balompie at Camp Nou on August 20, 2016 in Barcelona, Spain. (Photo by Alex Caparros/Getty Images)
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Lionel Messi’s “return” to the Argentinian national team may have to wait.

Barcelona has revealed their superstar picked up a left hamstring injury at an unspecified time, and discovered them during tests earlier on Monday. The statement said he would still travel to Argentina to link up with the national team for the international break, and will have more tests there.

Argentina, sitting in the third spot in CONMEBOL World Cup qualifying and just two points above elimination, have vital matches against Uruguay and Venezuela over the next week. “His presence in those matches will depend on how the injury develops,” the statement from Barcelona read.

It is unclear when Messi developed this injury. He has played the full 90 minutes in all four of Barcelona’s matches this season, including the 1-0 win over Athletic Bilbao on Sunday, the first of the four matches in which he did not score or assist a goal.

This also could be a bit of gamesmanship from Barcelona. Obviously, it benefits clubs for their players to rest during international breaks instead of play international matches, and for them to suddenly announce an injury to Lionel Messi would put pressure on Argentina to consider sitting their superstar. Of course, in attempts to dispel this idea, Barcelona included in their statement that the injury report was “approved by the FC Barcelona Medical Services and the Argentinian Football Association.”

A legitimate injury to Messi would be a devastating blow to Argentina considering Sergio Aguero has already withdrawn from the squad following an injury picked up against West Ham this weekend. Aguero was substituted in the 88th minute of Manchester City’s 3-1 win over the Hammers.

Messi was expected to make his first appearance to the national team setup after his brief “retirement” following the loss in the Copa America finals.

VIDEO: What will Southampton’s new star Boufal provide?

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Sofiane Boufal is a name many will be familiar with.

After his $21 million move to Southampton on Monday for a club-record fee, plenty of people are getting excited about seeing Boufal in the Premier League.

The Moroccan international is the type of player who has already become a cult figure due to the “Football Manager” video game, as his potential to become a star of European soccer has been well documented with huge teams interested in signing him over the past six months.

[ MORE: Fabregas wants Chelsea stay ]

That’s because Boufal, 22, shone for Lille last season, scoring 12 goals and his trickery, pace, set pieces and direct running saw him named as the best African player in Ligue 1.

He chose Southampton and it seems like a very wise choice after they helped turn the likes of Sadio Mane, Adam Lallana and Luke Shaw, plus many more, into top international players.

So, what have Southampton got in Boufal?

Take a look at the video above which gives a great overview of Boufal from his time at Lille after making the step up from Angers in Ligue 2 in January 2015.

That’s right, those comparisons with Riyad Mahrez seem pretty legit.

Late show? Chelsea linked with transfer deals for James Rodriguez, Alonso

Photo by Gonzalo Arroyo Moreno/Getty Images
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Chelsea may be set to do some late business in the summer transfer window.

According to Marca in Spain they will sign Fiorentina defender Marcos Alonso for $27 million.

[ MORE: Boufal signs for Saints ]

Alonso, 25, previously played for Bolton and Sunderland in the Premier League but the Real Madrid product moved to Serie A in 2013 and has flourished for Fiorentina. He is able to operate as a left back and in midfield and could provide Antonio Conte with another option in defense so he can switch Cesar Azpilicueta to right back and potentially Branislav Ivanovic to center back.

Another player who could be on his way to Chelsea is Real Madrid’s forward is James Rodriguez. This is one we’ve heard before, many times.

The Colombian national team captain, 25, was subject of a $80 million bid from Chelsea but according to the Daily Mirror the bid was turned down by Real Madrid.

[ MORE: McCourt to buy Marseille ]

James has found himself a bit-part player at the Santiago Bernabeu with Cristiano Ronaldo, Gareth Bale and Karim Benzema around. However he has a huge release clause in his contract and Chelsea would have to pay close to $100 million for his services. Is he really worth that? When you have Oscar, Pedro, Willian, Eden Hazard, Victor Moses and others already in your squad, probably not.

In terms of outgoings at Stamford Bridge, Kurt Zouma has been linked with a move to Schalke in the Bundesliga as the French central defender continues his long comeback from a horrendous knee injury he suffered against Manchester United in February last season. Zouma, 21, is said to be close to joining Schalke on a season-long loan deal wit a view to a permanent move.

Nacer Chadli signs for West Brom

COLCHESTER, ENGLAND - JANUARY 30:  Nacer Chadli of Tottenham Hotspur celebrates scoring his team's third goal during the Emirates FA Cup Fourth Round match between Colchester United and Tottenham Hotspur at Weston Homes Community Stadium on January 30, 2016 in Colchester, England.  (Photo by Michael Regan/Getty Images)
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West Bromwich Albion have signed Nacer Chadli from Tottenham Hotspur in a deal said to be worth $17 million.

[ MORE: Boufal signs for Saints ]

Chadli, 27, has spent the past three seasons with Spurs after arriving from FC Twente in 2013 for $9.1 million.

The Belgian international fell down the pecking order at Tottenham last season under Mauricio Pochettino and has now moved on to secure regular minutes in the Premier League.

Speaking to West Brom’s website about his move to the Hawthorns, Chadli was delighted to be on board with Tony Pulis‘ side.

“I feel very good to be here. It came very quickly but I spoke to the Club and they have a good team, a good manager and I am very pleased to be here,” Chadli said. “My ambitions? I just want to help the team win as many games as possible.”

Chadli can operate in central midfield, out wide, in a No. 10 role or even up front and he is very good on the ball and has an eye for goal with 25 goals in 119 appearances in all competitions for Tottenham.

With Spurs possessing Dele Alli, Victor Wanyama, Dele Alli, Erik Lamela, Christian Eriksen and Heung-Min Son in the central and attacking midfield areas, Chadli wasn’t guaranteed minutes at White Hart Lane.

West Brom have picked up a player who can create chances and is a powerful presence in midfield. With his creativity Chadli should slot in nicely in front of Darren Fletcher in the Baggies’ midfield and Pulis will be hoping he can lay chances on for Salomon Rondon up top.

This seems like a really shrewd piece of business by West Brom, while Spurs are also looking to offload Ryan Mason and Son according to multiple reports. Is Pochettino lining up some last-minute business in the transfer window?

Could West Brom’s Saido Berahino be heading for Spurs with Chadli the sweetener in the deal? Let’s see what the next 48 hours or so brings before the transfer window slams shut at 6 p.m. ET on Wednesday.