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.

Sir Alex’s son in trouble for saying he’d “shoot” refs

Photo by Dan Kitwood/Getty Images
Leave a comment

LONDON (AP) It clearly runs in the family.

Former Manchester United manager Alex Ferguson was known for having an explosive temper during his nearly 27 years at Old Trafford, and it seems he has passed it down to his son.

Darren Ferguson, who is the manager of third-tier English team Doncaster, is in trouble for saying he would “shoot” referees because of what he perceived as their poor standards.

Ferguson was charged by the English Football Association on Wednesday for remarks that “were improper and/or brought the game into disrepute.”

The 45-year-old coach has already apologized, saying it was a “tongue-in-cheek comment” and that “I do not advocate violence against officials.”

Ferguson was unhappy his team was denied a penalty in a 1-1 draw with Plymouth on Saturday.

“The referees are part-time and the standard is appalling, their fitness levels are a disgrace, I’ve had enough of it,” Ferguson said after the match.

“What can I do? Shoot them, it would be a good idea.”

Follow Live: Chelsea, Swans, Cherries in FA Cup replays

Photo by Paul Gilham/Getty Images
Leave a comment

Chelsea, Swansea City, and Bournemouth look to avoid upsets in replays of their third round FA Cup matches.

[ LIVE: Follow all the FA Cup scores here ]

All three matches kick off at 2:45 p.m. ET

The Blues tangle with former Premier League peers Norwich City, this time at Stamford Bridge, in a bid to host a fourth round match with Newcastle United.

Antonio Conte‘s not messing around (too much) with the XI.

Swansea City and Wolves, meanwhile, are arguably battling for a bid in the fourth round, as a trip to Notts County is on the docket for the winner of Wednesday’s replay at the Liberty Stadium.

Bournemouth is at Wigan Athletic for a replay with the third-tier Latics, with the victor hosting West Ham United on Jan. 27.

Benevento captain Lucioni banned one year for doping

Photo by Maurizio Lagana/Getty Images
Leave a comment

ROME (AP) Benevento captain Fabio Lucioni has been banned one year for doping.

[ MORE: Plenty to prove for Big Sam ]

Italy’s national anti-doping organization made the decision Tuesday after the steroid clostebol was found in a sample taken after Benevento’s 1-0 loss to Torino in September.

Benevento team physician Walter Giorgione was banned for four years for administering the steroid to Lucioni in a spray.

Both Lucioni and Giorgione plan to appeal.

The 30-year-old Lucioni joined Benevento in 2014 and the defender helped the team move from the third division up into Serie A this season for the first time.

Benevento is last in Serie A with only two wins in 20 matches.

The ban is back-dated to October, meaning Lucioni can return early next season.

Everton completes move for Walcott: “I’m dead excited” (video)

@everton
Leave a comment

Everton continues to supply its managers with top-end talent, adding Theo Walcott to its expensive season of boys which includes Gylfi Sigurdsson, Wayne Rooney, Cenk Tosun, Jordan Pickford, and Michael Keane.

[ MORE: Plenty to prove for Big Sam ]

The deal is reported to be near $28 million for Walcott, who’s made only a half-dozen Premier League appearances this season but did nab three goals in five Europa League matches.

Walcott, 28, scored 108 goals in 397 appearances for the Gunners. His 19-goal campaign last season was his second-best — he scored 21 in 2012-13 — but Walcott dipped down Arsene Wenger‘s depth charge and is leaving to pursue regular football.

And his comments will be lapped up by the #WengerOut brigade at his now former club:

“The Club has won trophies but I want them to win trophies now. The manager is very hungry and it’s just what I need. I’ve had a couple of chats with him and straightaway I felt that hunger and that desire that he wanted from me. I need that and I wanted that

The move is another exciting one for Everton, which has underachieved under Ronald Koeman and now Sam Allardyce. And it’s another sale from Arsenal which gives pause: Are the underperforming Gunners going to regret the move?

In the 2005-06 season, Walcott made his Southampton debut in the Football League Championship at the age of 16, and moved to Arsenal the next season.

Walcott has eight goals in 47 caps for England, and won two FA Cups at Arsenal.

[ MORE: Montreal nabs Algerian DP ]

Here is a useful quote from Sam Allardyce:“His physical output is excellent, he would be one of our top players in that area as well, which will hopefully bring us a lot more excitement and more ability to get forward quicker and create.

And here is an utterly useless one: ““If you analyse his goal record, then we are looking at a player who contributes goals on a regular basis.”

You don’t say. To paraphrase: If you look at all his goals, he regularly scores goals. Here’s more from the player on his move.