Apr 23, 2012, 1:36 PM EST
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.
Dec 11, 2013, 6:11 PM EST
Tough draws await Arsenal, Manchester City in the knockout round.
Dec 11, 2013, 5:31 PM EST
Demba Ba’s 10th minute goal was enough to give Chelsea Group E.
Dec 11, 2013, 4:47 PM EST
Brazilian star’s hat trick helps Barcelona rout Celtic, claim first in Group H.
Dec 11, 2013, 4:43 PM EST
One good club from Group F was bound to be odd team out on Wednesday as Champions League group play finished with a high-wire tension.
Dec 11, 2013, 3:32 PM EST
There’s more to “coaching discussions” right now in domestic soccer than those four MLS openings:
Dec 11, 2013, 2:31 PM EST
He keeps performing for “club” … but when it will translate to performance for “country?”
Dec 11, 2013, 2:15 PM EST
Hull chairman Assem Allam is ready to risk backlash with choice comments and a formal application for name change.
Dec 11, 2013, 1:45 PM EST
From East Coast goalkeeper to West Coast coach in under five hours.
Dec 11, 2013, 1:28 PM EST
Which venues will the USA be playing in next summer? We take an in-depth look at them, right here:
Dec 11, 2013, 1:12 PM EST
Next stop: politicians. David Beckham’s bid for a stadium in Miami is moving ahead.
Dec 11, 2013, 12:34 PM EST
New York City FC is on the verge of getting a palace in the Bronx.
Dec 11, 2013, 12:09 PM EST
What? Roy Keane back down from a fight? Sir Alex and Keano still bitter after all these years.
Dec 11, 2013, 11:33 AM EST
Dwyer suggested a transfer abroad was imminent, but has backtracked.
Dec 11, 2013, 10:54 AM EST
Longtime Revs keeper and Boston Marathon bombing hero retires with 75 clean sheets and 110 wins.
Dec 11, 2013, 10:15 AM EST
Former Inter star sends Juve down to the Europa League with help from Didier Drogba.
Dec 11, 2013, 10:00 AM EST
Who’s hot and who’s not? Check out how the sides stack up after a double dose of action last week:
Dec 11, 2013, 9:50 AM EST
Any takers on these three countries as potential upset-springers in Brazil?
Dec 11, 2013, 8:52 AM EST
Could Newcastle set a standard in offering exclusive access to paying media members?
Dec 11, 2013, 8:31 AM EST
Has Wayne Rooney rejected contract talks with Manchester United? Can a suitor pry Vincent Kompany from City? All this and more in Wednesday’s transfer rumor roundup.
Dec 11, 2013, 7:41 AM EST
Man City boss Manuel Pellegrini and goal scorer James Milner apparently in dark over UEFA Champions League tiebreaking rules.
- Demba Ba’s goal enough to give Chelsea 1-0 Champions League win, first place in Group E 0
- Neymar’s first three Champions League goals see Barcelona to 6-1 win, top of Group H 0
- Arsenal advance in Champions League, but Napoli out despite win 0
- Venue Guide: Check out where the USA will play at 2014 World Cup in Brazil 5
- Premier League Power Rankings: Everton flying, Manchester United nosedive – Week 14-15 1
- Three 2014 World Cup dark horses across three continents 3
- 2014 World Cup Draw: Recapping the event (43)
- 2014 World Cup Draw: USA in Group of Death with Germany, Portugal, Ghana – Schedule, times, venues (34)
- What US Soccer wants from the World Cup draw (23)
- Now that we know the U.S. opponents, which 23 players should Jurgen Klinsmann bring to Brazil? (21)
- Sporting Kansas City crowned 2013 MLS champions after 10 rounds of penalty kicks (16)
- Watch Out Netherlands! Chile-Clan Ain't Nothin' to Mess With!
- Messi on Safe Track to Full Recovery
- The Argentinian Armada, Favorites for Brazil 2014
- Brazil 2014: A Look At South America
- Arena de Amazonia: Host of USA vs CR7
- USA Will Advance in Brazil
- Group B: No Walk In The Park
- Analyzing The Draw From An Azzurri Viewpoint
- Q&A With Alvaro Saborio
- Ronaldo: "I Didn't See the Draw, I Was Asleep"