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.

MLS Snapshot: Chicago Fire 1-3 Toronto FC (video)

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The game in 100 words (or less): Greg Vanney and Toronto keep on doing their thing, and the Canadian side is yet another step closer to achieving MLS glory. TFC picked up its 50th point of the season on Saturday night after comfortably handling the Chicago Fire, who have cooled off significantly as of late in the Eastern Conference. The Fire are now nine points behind the East leaders and are losers of four of their last five matches.

Three moments that mattered

54′ — Accam, Fire level it up — Toronto really does manage to get contributions from everybody…

64′ — Hasler nets first MLS goal — Toronto really does manage to get contributions from all of their players…

90′ — Giovinco says goodnight to Chicago — That’s 12 goals on the season for Sebastian Giovinco and the TFC striker continues to help his side push towards the top seed in the East and MLS.

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Man of the match: Sebastian Giovinco

Goalscorers: Marco Delgado (14′), David Accam (54′), Nick Hasler (63′), Sebastian Giovinco (90′)

Video: Watts gifts D.C. United own goal for the ages

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Not many things have gone right for either side involved in 2017, but D.C. United was the recipient of a gift early on against the Colorado Rapids on Saturday night.

[ MORE: Piatti brace lifts Impact to fourth win in a row; Orlando, Crew draw ]

In the 27th minute, Rapids center back Jared Watts received the ball at the back, before making a routine back pass to USMNT goalkeeper Tim Howard

Or at least, it should have been a routine back pass.

Instead, Watts’ pass was well off target and too strong for Howard to reach and landed in the back of the Rapids goal. 1-0 in favor of D.C.

Reminder: Both these teams sit at the bottom of their respective conferences on points.

MLS Snapshot: Piatti brace lifts Impact | Crew, Orlando City draw

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The game in 100 words (or less): The Montreal Impact have proven to be a second-half of the season team the last several years, and that form appears to be holding true once more. Mauro Biello’s side won its fourth straight match on Saturday, while Ignacio Piatti continues to show he’s one of the most deadly scorers in the league. Meanwhile, RSL’s six-match unbeaten run is snapped north of the border, leaving the Western Conference side three points out of sixth place.

Three four moments that mattered

11′ — Piatti nets his first of the night — The Impact made this attack look so easy, and Ignacio Piatti simply won’t miss a chance like this one.

26′ — Evan Bush left motionless as RSL equalize — Luis Silva took matters into his own hands, and boy did he connect with this effort!

29′ — Impact punish poor RSL defense — Guess who? Piatti has his second of the evening.

47′ — Hosts begin to pile it on — Anthony Jackson-Hamel played provider in the first two goals, so it’s only fair he got one of his own.

[ FOLLOW: All of PST’s MLS coverageStandings | Stats | Schedule ]

Man of the match: Ignacio Piatti

Goalscorers: Ignacio Piatti (11′, 29′), Luis Silva (26′), Anthony Jackson-Hamel (47′)


The game in 100 words (or less): Orlando City and the Crew settled for a point apiece on Saturday night, but for the former the club is running out of opportunities to pick up points in the playoff race. Giles Barnes pulled a goal back for the hosts after Lalas Abubakar netted his first MLS goal for the Crew, but Orlando couldn’t find a second. The Lions played up a man for the final 13 minutes, following Harrison Afful’s dismissal.

Three moments that mattered

35′ — Abubakar knocks in first MLS goal — Orlando City’s defensive woes are certainly notable as well, but for Lalas Abubakar this is a quality way to open his scoring account in MLS.

67′ — Barnes knots it up at 1-1 — The veteran MLS forward picked up his second goal of the season.

77′ — VAR used for red card decision — The video monitor came into play briefly in the second half, and Harrison Afful was sent off the pitch early after the referee viewed the defender’s elbow to the head of Yoshi Yotun.

[ FOLLOW: All of PST’s MLS coverageStandings | Stats | Schedule ]

Man of the match: Zack Steffen

Goalscorers: Lalas Abubakar (35′), Giles Barnes (67′)

Atlanta United fans pack 20,000 into new stadium for training session

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Atlanta United is currently in the midst of a three-match road trip in MLS play, but that didn’t stop the club from unveiling its new home venue to a massive crowd of supporters on Saturday.

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Over 20,000 fans of the Eastern Conference expansion side filed into Mercedes-Benz Stadium to watch Gerardo Martino’s side train on Saturday as Atlanta prepares to finish out its road trip against D.C. United and the Philadelphia Union.

Atlanta will open up home play at their new stadium on September 10 when they host FC Dallas. The club will have the benefit of playing eight of its final 10 regular season matches in front of its Georgia fan base.

The first-year MLS side will share the stadium with the Atlanta Falcons of the NFL.

Here are some sights from the training session