Skip to content

Compromised numbers: Why the statistic you see may not be actual possession

Apr 23, 2012, 1:36 PM EST

Barcelona's midfielder Xavi Hernandez re Getty Images

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.

Latest Posts
  1. Van Gaal hails win over Newcastle as “maybe our best match of the season”

    Mar 4, 2015, 5:38 PM EST

    Britain Soccer Premier League AP

    Manchester United needed a gift from opposing goalkeeper Tim Krul, but Louis van Gaal loved his club’s performance on Wednesday.

  2. Roberto Martinez blames fatigue for Everton’s struggles; have “10 cup finals” to survive

    Mar 4, 2015, 5:37 PM EST

    FBL-ENG-FA CUP-EVERTON-WEST HAM Getty Images

    After their 12th defeat of the season, the Toffees after sinking towards the bottom three.

  3. Liverpool 2-0 Burnley: Reds cruise with Henderson at the helm

    Mar 4, 2015, 5:10 PM EST

    21a48a639b225b2f6c349a47a6799b1d Getty Images

    Burnley’s loss leaves them 19th, in the drop zone with 22 points.

  4. Tottenham Hotspur 3-2 Swansea City: Lloris saves it late for Spurs

    Mar 4, 2015, 5:00 PM EST

    Britain Soccer Premier League AP

    Swansea sit ninth with 40 points, while Spurs sit 7th place. Tottenham is four points behind No. 5 Liverpool.

  5. Stoke City 2-0 Everton: Moses, Diouf pile more misery on the Toffees

    Mar 4, 2015, 5:00 PM EST

    Potters continue to climb up the table, as Toffees head in the opposite direction.

  6. West Ham United 0-1 Chelsea: Hazard’s header enough for league leaders

    Mar 4, 2015, 4:53 PM EST

    Chelsea stay top after hard-fought win at Upton Park.

  7. Queens Park Rangers 1-2 Arsenal: Red-hot Giroud helps Gunners to win

    Mar 4, 2015, 4:50 PM EST

    Queens Park Rangers v Arsenal - Premier League Getty Images

    It’s now five goals from his last five games for the Frenchman.

  8. Newcastle United 0-1 Manchester United: Krul gaffe spoils Jonas return

    Mar 4, 2015, 4:40 PM EST

    TIm Krul Getty Images

    Manchester United remains fourth, one point behind third place Arsenal, while Newcastle is still comfortably in 11th place with 35 points.

  9. LIVE – Premier League, at the half: Chelsea, Man City, Liverpool ahead

    Mar 4, 2015, 3:49 PM EST

    FBL-ENG-PR-WEST HAM-CHELSEA FBL-ENG-PR-WEST HAM-CHELSEA

    Seven games are going on in the PL on Wednesday, watch the second half of every match right here.

  10. Swansea’s Bafetimbi Gomis stretchered off the pitch after appearing to collapse

    Mar 4, 2015, 3:09 PM EST

    Gomis Getty Images

    Swansea’s French striker carried off the pitch after appearing to collapse at White Hart Lane.

  11. Agent says Dani Alves “in advanced talks” with other club

    Mar 4, 2015, 3:07 PM EST

    463262876 Getty Images

    Dani Alves is all but out at Barcelona, but where will the Brazilian back end up?

  12. Watch Live: Liverpool vs. Burnley (Lineups and Live Stream)

    Mar 4, 2015, 2:28 PM EST

    Burnley v Liverpool - Premier League Getty Images

    The Reds are unbeaten in their last 11 league matches, a run they will look to continue against a Burnley side sitting in the drop zone.

  13. Watch Live: Tottenham Hotspur vs. Swansea City (Lineups and Live Stream)

    Mar 4, 2015, 2:16 PM EST

    Swansea City v Tottenham Hotspur - Premier League Getty Images

    Only one spot separates the two sides on the table, giving every point some added value at White Hart Lane.

  14. Watch Live: Stoke City vs. Everton (Lineups and Live Stream)

    Mar 4, 2015, 2:15 PM EST

    FBL-ENG-PR-EVERTON-QPR FBL-ENG-PR-EVERTON-QPR

    Who will win the battle of the USMNTers. Geoff Cameron or Tim Howard?

  15. Watch Live: Manchester City vs. Leicester City (Lineups and Live Stream)

    Mar 4, 2015, 2:07 PM EST

    Kompany Getty Images

    Can the Citizens keep their faint title hopes alive? Watch live online, here.

  16. Watch Live: Queens Park Rangers vs. Arsenal (Lineups and Live Stream)

    Mar 4, 2015, 2:04 PM EST

    Arsenal v Queens Park Rangers - Premier League Getty Images

    It’s a top-three vs. bottom-three battle as the Gunners travel to Loftus Road to face a QPR side fighting for Premier League survival.

  17. Watch Live: West Ham United vs. Chelsea (Lineups and Live Stream)

    Mar 4, 2015, 2:01 PM EST

    Chelsea v Tottenham Hotspur - Capital One Cup Final Getty Images

    A ding-dong London derby at Upton Park. Can the Hammers derail Chelsea’s title charge? Watch live online, here.