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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.

Southampton 4-2 Manchester City: Southampton carves up City behind Mane hat-trick, Tadic service

during the Barclays Premier League match between Southampton and Manchester City at St Mary's Stadium on May 1, 2016 in Southampton, England.
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Manchester City clearly had one eye on the Champions League semifinals. It came at the expense of their chances to remain in the competition next year.

The visitors at St. Mary’s had the opportunity to lock up Champions League play next season with all three points, but instead Manuel Pellegrini rested a number of starters including Sergio Aguero and Kevin De Bruyne, and Southampton ripped them apart in a 4-1 win. Saido Mane grabbed a hat-trick and Dusan Tadic had a trio of assists as their attack swarmed a mistake-prone and clearly distracted Manchester City.

Both sides had spells in the opening 20 minutes, but Southampton appeared more dangerous. Shane Long made multiple appearances in front of the Manchester City goal, picking the pocket of Pablo Zabaleta to earn a corner on 15 minutes and shooting just wide of the near post in the 19th minute.

Frasier Forster was required to keep the game scoreless in the 20th minute as Kelechi Iheanacho stole the ball from Virgil van Djik on the touchline and found Raheem Sterling in space inside the box, but his shot was saved expertly by Forster.

[ MORE: Watch full PL match replays ]

It would be the in-form Long to take the lead in the 25th minute on a beautiful bit of play. A fantastic ball over the top of the City defense fell to a streaking Dusan Tadic, and his flick over the top met a sliding Shane Long, who beat Nicolas Otamendi for the opener.

They’d get a second just four minutes later on yet another sweet-looking goal, with Tadic getting yet another assist with a perfectly weighted ball for Saido Mane, who smacked it by Joe Hart from a tight angle.

[ MORE: Latest Premier League standings ]

Southampton continued to press and hold much of the meaningful possession, but Manchester City refused to capitulate, scoring a lifeline before halftime. With the ball in the Southampton penalty area, Cuco Martino saw the ball skip off his thigh and pop into the air, where Iheanacho latched onto it and headed it into the net.

[ MORE: Full lineups, stats, box score ]

It was a tough way for the hosts to go into halftime, as they had dominated much of the first half, but no matter, as they made amends. Following the break, Southampton restored their two-goal lead off a corner in the 57th minute as Van Djik’s header was tipped by Joe Hart off the crossbar. Jose Fonte whiffed at the rebound but Mane was there from point blank range to give Southampton a 3-1 lead.

Mane would complete his hat-trick in the 68th minute. Van Djik won the ball in the Southampton half to start the break, and Tadic picked up his third assist of the match as he slotted Mane through on goal for yet another clinical finish.

Manchester City got another back as Iheanacho bagged his second in the 79th minute with a wonderful curler from outside the box, but it was too little too late for the visitors.

Both teams fought until the final whistle, and it could have cost Jesus Navas his fitness as the Argentinian seemingly picked up a serious limp in the final few minutes.

VIDEO: Claudio Ranieri says he might miss Leicester City winning the Premier League

MANCHESTER, UNITED KINGDOM - MAY 01:  Claudio Ranieri, manager of Leicester City applauds the fans after the Barclays Premier League match between Manchester United and Leicester City at Old Trafford on May 1, 2016 in Manchester, England.  (Photo by Laurence Griffiths/Getty Images)
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Following Leicester City’s gritty draw with Manchester United at Old Trafford, the Foxes missed out on securing the Premier League trophy, but come tomorrow evening, they could still be celebrating.

With the point against United, their magic number is now two, meaning any dropped points by Tottenham wins Leicester City the league title. Tottenham travels to Stamford Bridge tomorrow to take on Chelsea, and should they fail to win, the trophy is Leicester’s.

But manager Claudio Ranieri, the hero in Leicester for guiding their beloved club to the unthinkable, might be the last to find out.

In his post-match comments, Ranieri said he could be on a plane during the Spurs game, therefore unable to find out the result until he lands. The reason? He’s going back to Italy to have lunch with his 96-year-old mother.

“I would like to watch to watch the match,” Ranieri said. “But I think I am on the flight back from Italy, and then it’s difficult for me to watch the match. Maybe when I landed, I will know the result.”

What a family man. No wonder his team plays like a close-knit unit.

AC Milan fights back for draw against Frosinone, but still falls out of European place

MILAN, ITALY - MAY 01:  Mario Balotelli of AC Milan reacts during the Serie A match between AC Milan and Frosinone Calcio at Stadio Giuseppe Meazza on May 1, 2016 in Milan, Italy.  (Photo by Marco Luzzani/Getty Images)
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AC Milan fought back from down 3-1 to earn a point at home against relegation candidate Frosinone, but by dropping points they’ve also dropped out of a European position.

Frosinone got goals from Oliver Kragl and Luca Paganini in the first half, and Federico Dionisi struck in the 54th minute to go 3-1 up. But Luca Antonelli scored in the 74th minute – just a minute after coming on for AC Milan – and Jeremy Menez finished a penalty in added time to pull level.

The draw, coupled with a 1-0 Sassuolo win against Verona, dropped the Rossoneri to 7th in the Serie A table, out of the Europa League places. They sit on 54 points, with Sassuolo on 55.

Contributing heavily to the final result was Frosinone goalkeeper Francesco Bardi, who saved a Mario Balotelli penalty and produced a host of acrobatic first-half saves to keep the Milan attack at bay.

AC Milan hardly has time to lick its wounds, with just three matches remaining, two against Juventus and Roma to close out the year. Meanwhile, the point for Frosinone is important but likely not enough as they fall four points back of Palermo who Sampdoria.

Watch Live: Southampton vs. Manchester City (Lineups & Live Stream)

MANCHESTER, ENGLAND - NOVEMBER 28:  Raheem Sterling of Manchester City and Victor Wanyama of Southampton compete for the ball during the Barclays Premier League match between Manchester City and Southampton at the Etihad Stadium on November 28, 2015 in Manchester, England.  (Photo by Alex Livesey/Getty Images)
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Manchester City has shuffled the deck, with five changes from last time out as Manuel Pellegrini and company travel to St. Mary’s to take on Southampton, live at 11:30 a.m. ET on NBCSN or live online at NBC Sports Live Extra.

Sergio Aguero is on the bench, while Kevin De Bruyne is not selected at all for City as Wilfried Bony is the man up top along with Kelechi Iheanacho in support. Jesus Navas is also among the substitutes, with Samir Nasri and Raheem Sterling among the starters.

WATCH LIVE: Southampton vs. Manchester City live online at NBC Sports Live Extra

David Silva is not included in the squad having suffered a hamstring injury, and while Yaya Toure has returned to fitness, he is not among those named.

For Southampton, three changes from their 4-2 win over Aston Villa dot the map, with Cuco Martina, Jordy Clasie, and Saido Mane all coming into the side. Charlie Austin is on the bench having returned from a hamstring problem, but Shane Long gets the nod to start, while Graziano Pelle does not appear.

A win for Manchester City would put them firmly in fourth at 67 points, seven clear of Manchester United with two more games to play.

LINEUPS

Southampton: Forster; Martina, Fonte, Van Dijk, Bertrand; Clasie, Wanyama, S.Davis, Tadic, Manè; Long.
Subs: Stekelenberg, Yoshida, Soares, Romeu, Ward-Prowse, Rodriguez, Austin.

Manchester City: Hart, Zabaleta, Otamendi, Mangala, Kolarov, Delph, Fernandinho, Nasri, Sterling, Iheanacho, Bony
Subs: 
Caballero, Sagna, Clichy, Demichelis, Fernando, Navas, Aguero