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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.

Gerrard urges Liverpool to “try and bid for Van Dijk”

SOUTHAMPTON, ENGLAND - DECEMBER 28:  Virgil van Dijk of Southampton celebrates as he scores their first goal during the Premier League match between Southampton and Tottenham Hotspur at St Mary's Stadium on December 28, 2016 in Southampton, England.  (Photo by Julian Finney/Getty Images)
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Virgil Van Dijk‘s quick rise in the Premier League has caught the attention of many around England, and one of the division’s greats has high hopes the Dutchman will join his former side in the future.

[ MORE: Saints wallop Leicester in complete effort ]

Steven Gerrard has suggested that Liverpool come out and pursue Van Dijk, who joined Southampton back in 2015 from Scottish side Celtic.

Gerrard — who is set to take a coaching position with Liverpool’s academy — believes the budding star would be a strong fit for the Reds, however, the ex-midfielder realizes it’ll be a hard sell.

“Who I think we need, I would go and try and bid for Van Dijk from Southampton,” Gerrard told BT Sport. “But we’ve had enough of their players so that will probably go down like a lead balloon.”

The 25-year-old has made waves in England’s top flight after quickly proving to be one of the division’s top defenders and helping guide the Saints towards the top half of the table since his arrival.

Report: San Diego making push to become future MLS expansion site

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With the NFL no longer the biggest show in town, San Diego could be bringing another football to the city in the near future.

[ MORE: USMNT’s Hyndman provides assist in Rangers debut win ]

According to NBC 7 San Diego, FS Investors founder Mike Stone and former Qualcomm Vice Chairman Steve Altman are prepared to reveal their proposal on Monday that will bring a future MLS franchise to San Diego.

[ FOLLOW: All of PST’s MLS coverage ]

The proposed move includes a stadium plan that will reside where the Chargers’ Qualcomm Stadium currently sits. With the NFL franchise now playing in Los Angeles, the San Diego Padres of Major League Baseball are the only remaining professional team in the area, out of the five major sports in the U.S.

NBC 7 is also reporting that a future San Diego team would share its facility with the San Diego State Aztecs football team.

MLS is currently up to 22 teams entering the 2017 season, while Los Angeles FC is also tabbed to enter the league next year. David Beckham’s Miami project is also considered to be the league’s 24th team, and MLS is likely to hold off on further announcements regarding expansion until later in 2017.

If San Diego were to be chosen as an expansion site, the club would become the fourth to call California home in the current state of MLS, joining the San Jose Earthquakes, Los Angeles Galaxy and LA FC (2018).

In addition to San Diego, several other cities are currently vying to enter MLS in the future, including St. Louis, Cincinnati, Sacramento and Charlotte.

Hull’s Ryan Mason hospitalized following collision with Gary Cahill

LONDON, ENGLAND - JANUARY 22: Ryan Mason of Hull City lies injured after the collision with Gary Cahill of Chelsea during the Premier League match between Chelsea and Hull City at Stamford Bridge on January 22, 2017 in London, England.  (Photo by Richard Heathcote/Getty Images)
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Ryan Mason has undergone surgery following a scary collision with Chelsea’s Gary Cahill on Sunday.

[ MORE: Chelsea goes eight points clear at top of PL ]

The Hull City midfielder was injured after knocking heads with Cahill during first half of the 2-0 defeat to the Blues. Nine minutes of first-half stoppage time were needed after Mason stayed down on the pitch at Stamford Bridge.

[ MORE: Xhaka’s red card makes him most sent-off player in Europe ]

It has been confirmed by the club that Mason suffered a skull fracture, while it is has also been speculated that the 25-year-old could have had bleeding on his brain.

Mason will remain hospitalized for the “next few days,” according to the Tigers.

“The Club can confirm that Ryan Mason sustained a skull fracture in our fixture at Chelsea this afternoon. He was taken to St Mary’s Hospital where he has undergone surgery.

“Ryan is in a stable condition and is expected to remain in hospital for the next few days.
“Everyone at the Club would like to express their sincere thanks for the excellent and swift care given to Ryan by both the Accident and Emergency department and Neurosurgery Unit at St Mary’s Hospital.

“A further update will be issued tomorrow.”

While Mason was forced off during the match due to the injury, Cahill managed to continue for Chelsea and scored the game’s second goal.

Watch: Scott Sinclair nets stunning curler in Celtic victory

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Celtic is enjoying another fine campaign in Scotland, and much of the team’s success can be attributed to the play of Scott Sinclair.

[ MORE: Burkina Faso, Cameroon progress at AFCON 2017 ]

The Englishman was at it again on Sunday during Celtic’s 3-0 Scottish Cup win over Albion Rovers when the 27-year-old curled an absolutely sublime effort into the top corner for the game’s opening goal.

The finish, Sinclair’s 13th of the season in all competitions, came after the winger picked up the ball on the left side of the Albion penalty area. Sinclair then proceeded to slot his dipping shot just under the bar and into the far post.

Celtic now moves on to the fifth round of this season’s tournament, joining the likes of Rangers and Aberdeen. In addition to the team’s success in the competition, the Bhoys have yet to lose a match in the Scottish Premier League this campaign (19 W, 1 D).