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

10 Comments

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.

Championship Focus: Bluebirds flying, Villa second-last

Photo by Harry Trump/Getty Images
Leave a comment

The wild 46-game slate that is the Football League Championship is already howling, with all 24 teams three matches deep into their campaigns toward Premier League promotion (or avoiding relegation to League One).

The three clubs relegated from the Premier League last season all sit within the Top 8 after three match days. Sunderland is unbeaten with a win and two draws, while Hull City is 1-1-1.

[ MORE: Barcelona falls to Real… again ]

Middlesbrough has two wins from three matches, three points behind three sides who’ve started a perfect 3-0.

Wolves and Ipswich Town are two of the three, and Cardiff City leads the way. Owner Vincent Tan has seen his club score six goals without conceding once in defeats of Burton Albion, Aston Villa, and Sheffield United.

Burton is 0-3, while Steve Bruce‘s Villa is just one point better and sits 23rd.

As for individual superlatives, Bristol City’s Bobby Reid has four goals to lead the league while familiar names Lewis Grabban (Sunderland) and Abel Hernandez (Hull City) are among a quartet of players to score thrice.

Meanwhile, PL transfer target Jota of Brentford continues to impress with three assists through three matches. Will he remain in the second tier by the close of the transfer window?

MLS Snapshot: Montreal Impact 3-0 Chicago Fire

Paul Chiasson/The Canadian Press via AP
Leave a comment

The game in 100 words (or less)Ignacio Piatti is very good at soccer, and Chicago backstop Matt Lampson is going to see him deep into his dreams. Piatti beat Lampson up close on a turnover and then, with Montreal ahead 2-0 off a PK, the Argentine curled a surprise shot from distance around the keeper. Game, set, match, and it wasn’t even halftime. The loss keeps Chicago from using its match-in-hand to catch second place New York City FC, while the three points move Montreal to within two points of the East’s final playoff position.

Three moments that mattered

6′ — Piatti starts the party — Gifted a chance with the keeper by a sloppy missed clearing attempt, the Argentine deftly pops the ball over Fire keeper Matt Lampson.

36′ — Lampson hurts his cause — Chicago’s backstop wasn’t at fault on the opening goal, but he was for the second. After chopping down Matteo Mancosu in the box, Lampson guessed wrong on the striker’s penalty kick and the Fire went down 2-0.

38′ — It’s not your night, Lamps — Pretty sure you can anyone named Lampson, Lamps. Anyway, this time it was one of MLS’ top newcomers who set up Piatti for a goal. “Nacho” has his 12th of the season thanks to Blerim Dzemaili, and my goodness did Piatti do well here.

Man of the Match: Piatti.

Forbes ranks the top supporters in Major League Soccer

Photo by Steve Dykes/Getty Images
Leave a comment

Forbes claims the shared honor will give two Cascadia Cup rivals one less thing to argue about, but we completely disagree.

The celebrated magazine says their metrics show the Portland Timbers and Seattle Sounders tied for the honor of who has the best fans in Major League Soccer.

The post says the determination was made through four factors: attendance, local TV ratings, merchandise sales, and social media followers on Twitter, Facebook, and Instagram.

Attendance was weighted heaviest, which certainly gives Atlanta United hope to go charging up the rankings in the future. For now, the “Five Stripes” are not included in the list.

The Galaxy finish third in the rankings, while the sixth-place New York Red Bulls edge New York City FC by one spot.

For the report and full explanation, head here.

Europa League preview: Everton, Milan, Marseille take next steps

Photo by Alex Livesey/Getty Images
Leave a comment

The UEFA Europa League playoff round takes full flight Thursday, a day after Utrecht struck a blow for the Eredivisie with a 1-0 win over Zenit Saint-Petersburg in a Wednesday first leg.

Premier League participants Everton will be seeking a result at home against Hajduk Split, the third-place team from Croatia’s top flight.

Gylfi Sigurdsson passed his medical at Goodison Park but will not be available for Everton on Thursday.

[ MORE: Barcelona falls to Real… again ]

As for the match, manager Ronald Koeman knows the Thursday matchdays for the UEL will try his club’s endurance and depth. From EvertonFC.com:

“We know English teams have some problems. I think it is more mental than physical because if you play in the Champions League – so Wednesday and Saturday – you have the same amount of days to recover. I try to put out the strongest team to start the game. That will take into account the tactical aspects of each game. That will mean different players start and different options in terms of substitutions.”

Captained by Zoran Nizic and managed by Joan Carrillo, Hajduk has a young star in the making in the form of 19-year-old attacking midfielder Nikola Vlasic, but Everton is heavily favored at home with Hajduk given 12:1 odds by bookmakers.

[ MORE: Barca GM says Coutinho, Dembele “close” ]

Those numbers are a relative sure thing compared to AC Milan’s visitors. Macedonia club Shkendija are a 33:1 underdog for its trip to Italy.

Elsewhere, Slovenian side Domzale is a longshot at home to visiting Marseille.

Speaking of bookmakers, Arsenal won’t enter the competition until the group stage but is considered the favorite to win the UEL by a hair over Milan. Everton, Villarreal, and Athletic Bilbao are level with third-best odds.

UEFA Europa League playoff first legs
Utrecht 1-0 Zenit — Weds.
BATE Borisov vs. Oleksandriya — 1 p.m. ET Thursday
Apollon Limassol vs. Midtjylland — 1 p.m.
Krasnodar vs. Red Star Belgrade — 1 p.m.
Dinamo Zagreb vs. Skenderbeu — 1 p.m.
FH vs. Braga — 1:45 p.m. ET Thursday
PAOK vs. Ostersund — 2 p.m. ET Thursday
Vardar vs. Fenerbahce — 2 p.m.
Plzen vs. AEK Lamaca — 2:15 p.m. ET Thursday
Altach vs. Maccabi Tel-Aviv — 2:30 p.m. ET Thursday
Ludogorets Razgrad vs. Suduva — 2:30 p.m.
Panathinaikos vs. Athletic Bilbao — 2:30 p.m.
Domzale vs. Marseille — 2:45 p.m. ET Thursday
Osijek vs. Austria Wien — 2:45 p.m.
Viitorul vs. Red Bull Salzburg — 2:45 p.m.
Ajax vs. Rosenborg — 2:45 p.m.
Legia Warsaw vs. Sheriff — 2:45 p.m.
AC Milan vs. Shkendija — 2:45 p.m.
Club Brugge vs. AEK — 2:45 p.m.
Partizan vs. Videoton — 3 p.m. ET Thursday
Everton vs. Hajduk Split — 3:05 p.m. ET Thursday
Maritimo vs. Dynamo Kyiv — 3:30 p.m. ET Thursday