Skip to content

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

Apr 23, 2012, 1:36 PM EDT

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. George John undergoes season-ending knee surgery

    Jul 31, 2014, 9:03 PM EDT

    George John 3

    Successful procedure marks the end of John’s 2014 hopes.

  2. For Napoli, hairstyle part of Marouane Fellaini’s appeal

    Jul 31, 2014, 8:12 PM EDT

    Fellaini Getty Images

    De Laurentiis confirms the partenopei’s interest in the afro-laden star.

  3. Clarence Goodson set to miss eight more weeks

    Jul 31, 2014, 7:22 PM EDT

    clarence_goodson Getty Images

    Toe injury to sideline the U.S. international for an estimated 10 games.

  4. Second thing Brian Ching doesn’t like: NWSL cooling breaks

    Jul 31, 2014, 6:31 PM EDT

    Brian Ching 2

    No. 1: Eddie Johnson. No. 2: These new-fangled rules.

  5. Talented US youngsters sign for Spanish sides Sevilla, Espanyol

    Jul 31, 2014, 6:02 PM EDT

    Sevilla

    Young Americans set to blaze trail in La Liga academies.

  6. Ignacio Piatti’s move to Montréal may cost him a place in Copa Libertadores’ final

    Jul 31, 2014, 5:39 PM EDT

    ignacio_perez_garcia AP

    San Lorenzo is in Copa’s finals, but Piatti is unlikely to join them.

  7. Can Stevan Jovetic, Scott Sinclair break into Manchester City’s lineup?

    Jul 31, 2014, 5:14 PM EDT

    International Champions Cup 2014 - Manchester City v Liverpool Getty Images

    Two players who spent plenty of time on the sidelines last season are pushing to be integral parts of Manuel Pellegrini’s plans.

  8. Matías Pérez García announced, becomes third Designated Player in San Jose history

    Jul 31, 2014, 4:42 PM EDT

    san_jose_earthquakes_logo

    29-year-old Argentina arrives from Tigre, becoming the club’s third Designated Player of all-time.

  9. Is Everton’s new striker Romelu Lukaku worth $47 million?

    Jul 31, 2014, 4:10 PM EDT

    Romelu Lukaku

    Everton’s frugality gave way to necessity. Is Lukaku worth it the serious cash they splashed?

  10. A list of Manchester United-linked names to consider in silly season

    Jul 31, 2014, 3:21 PM EDT

    twitter.com/officialsslazio twitter.com/officialsslazio

    Remember when Marco Reus, Dries Mertens and Leighton Baines solidified Manchester United’s status in Europe? Us neither.

  11. Rhode Island man sues Cristiano Ronaldo over CR7 trademark

    Jul 31, 2014, 2:56 PM EDT

    FBL-ESP-CUP-REALMADRID-ATLETICOMADRID Getty Images

    Cristiano Ronaldo and Christopher Renzi are looking horns over the CR7 trademark.

  12. Report: Ochoa to Malaga is on as Mexican goalkeeper replaces Caballero

    Jul 31, 2014, 2:25 PM EDT

    Guillermo Ochoa AP

    Guillermo Ochoa starred in the 2014 World Cup for Mexico, and now will try to fill Willy Caballero’s shoes at Malaga.

  13. Sierra Leone squad banned from traveling as Ebola virus spreads

    Jul 31, 2014, 2:08 PM EDT

    Sierra Leone Getty Images

    As deadly virus continues to spread, the Seychelles refuse to let Sierra Leone travel for qualifier.

  14. Video: Pepe spits on Keita; Latter claims past racial slur

    Jul 31, 2014, 1:50 PM EDT

    Ashley Cole, Pepe AP

    Seydou Keita has left Barcelona, but being in a different league has not stopped the animosity between the AS Roma midfielder and Real Madrid’s Pepe.

  15. Steven Gerrard: “Luis Suarez too good for Arsenal”

    Jul 31, 2014, 1:27 PM EDT

    Suarez and Gerrard both nominated for PFA award, as Liverpool dominate. AP

    Gerrard: “With all due respect to them, I said to Suarez that he was too good for Arsenal.”

  16. SI report: Bayern high on Julian Green, turned down PL loan offers

    Jul 31, 2014, 1:02 PM EDT

    Bayern Munich's Julian Green fights for the ball with Al-Merrikh's Ramadan Ajab during their friendly soccer match in Doha Reuters

    Bayern Munich chairman Karl-Heinz Rummenigge said several Premier League teams had interest in 19-year-old American striker Julian Green.

  17. Eddie Johnson response to Brian Ching’s criticism? “Scoreboard”

    Jul 31, 2014, 12:26 PM EDT

    South Korea v United States Getty Images

    Ching said his former USMNT teammate needs incentive-laden contracts to thrive, while Johnson claims Ching is jealous.

  18. Thursday transfer rumor roundup: Kljestan to Galaxy, USMNT’er to Crew?

    Jul 31, 2014, 11:42 AM EDT

    kljestan Getty Images

    Jermaine Jones is not the only US midfielder rumored to come home, while two Red Devils are tipped for Madrid.

  19. Testimony in death of Michigan referee provides disturbing glimpse into incident

    Jul 31, 2014, 10:52 AM EDT

    www.hometownlife.com (Bill Bressler) www.hometownlife.com (Bill Bressler)

    An altercation between a player and referee in a men’s league game left the official dead. What followed has been anything but pretty.

  20. Simeone praises Klinsmann’s US program that “seduces us as coaches”

    Jul 31, 2014, 10:03 AM EDT

    Portugal Champions League Soccer AP

    The World Cup praise has been flowing for Klinsmann in international circles, though American analysts like Alexi Lalas, Eric Wynalda and others have condemned the manager’s approach as too cautious.