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.

Sweden not keen on Zlatan’s World Cup return

Getty Images
Leave a comment

With Zlatan Ibrahimovic already making his mark in Major League Soccer with three goals in his first three games for the LA Galaxy, the veteran Swedish forward is eyeing a return to international duty for the 2018 World Cup this summer.

“A World Cup without me wouldn’t be a World Cup” said Ibrahimovic, 36, recently as he also confirmed during an appearance on the Jimmy Kimmel Show that he will be going to Russia but didn’t give specific details if it was as a spectator or a player.

Well, perhaps we won’t be having a World Cup because it appears not all of his former teammates would be on board if Zlatan took a U-turn on his decision to retire from the Swedish national team after EURO 2016.

Back-up goalkeeper Karl-Johan Johnsson had the following to say to outlet Main Oppose.

“We managed to qualify and go through to the World Cup without him, and I think we can manage to play well at the World Cup without him,” Johnsson said. “But it’s up to the coach to see if he wants to bring him – and I am sure if he does join, he will play well. As a team, we play as a collective, all the players together. With Zlatan, as a person, as a player he’s an individualist, and the play goes around him. Instead, now, we play more the team all together.”

Boom.

Zlatan has said multiple times that he is thinking about a return to the Swedish national team squad and with World Cup squads set to be announced in around about one month from now, surely Sweden’s head coach Janne Andersson must now if he will call up Zlatan.

The positives for Sweden are obvious. The can bring in their all-time leading goalscorer to jump off the bench late in tight games to try and get them out of Group F where they face Germany, Mexico and South Korea.

The negatives are centered around what Johnsson said, with Sweden looking like a tighter unit and all pulling together to get to the World Cup after missing out on qualifying for the last two in 2010 and 2014.

Zlatan has actually only played in two World Cups, in 2002 and 2006, scoring just once, and if he does go to the World Cup he will be taking the spot of one of Marcus Berg, John Guidetti, Ola Toivonen and Issac Thelin in the squad. Berg scored eight in qualifying, while Emil Forsberg scored four and the Swedish attacking unit seems to flow a lot better from Zlatan.

Look, Zlatan will probably go to the World Cup. But it appears not everyone will be happy with this decision.

PHOTOS: Tottenham’s stunning new stadium

Tottenham Hotspur
Leave a comment

Tottenham Hotspur’s new $1 billion stadium is taking shape and it is looking magnificent.

The plan is for Spurs’ new home at White Hart Lane to be ready for the 2018/19 season, with reports stating that Mauricio Pochettino‘s men will play their first couple of games away from home next season in order to squeeze in a few more weeks for construction.

Spurs’ new  home will seat 62,062 fans and will be the second-largest stadium in the Premier League behind Manchester United’s Old Trafford.

Take a look at the photos below in the spring sunshine in London, with the largest single-tier stand in Europe looking sublime as the roof panels are going on and the stadium is really starting to come to life.


Chelsea’s Marcos Alonso handed three-game ban

Getty Images
Leave a comment

After being named in the PFA’s Premier League Team of the Year on Wednesday, it has been a mixed few days for Chelsea’s Marcos Alonso as he has received a three-game ban with immediate effect after being found guilty of violent conduct.

Alsono, 27, stamped on Shane Long‘s calf in Chelsea’s 3-2 comeback win at Southampton last time out but referee Mike Dean missed the incident completely.

Since then Alonso has received a retrospective charge from the English FA and although the Spanish left back appealed the decision and the length of the ban, it was upheld and he will now miss Chelsea’s next three games.

Alonso will miss the clash at Burnley on Thursday, the FA Cup semifinal against Southampton on Sunday and the trip to Swansea City on Apr. 28.

Who will come in for Alonso?

Antonio Conte has already stated that Emerson Palmeri, a January arrival from AS Roma, will start at Burnley on Thursday and if the Brazilian full back impresses then it is highly likely he will stand in for Alonso in the big FA Cup semifinal on Sunday against Saints. Other options would be Davide Zappacosta playing as the left wing-back or even Cesar Azpilicueta out there.

As for Saints, they feel hard done by after Dean didn’t spot Alonso’s foul even though he was standing yards away from the incident and looking straight at it. At the time of the incident they led 1-0 going into half time and their manager Mark Hughes believes it would have made a big difference as Alonso’s cross set up Olivier Giroud to make it 2-1 and the Spaniard made a big difference from left back in the incredible 3-2 comeback victory. Still, at least Saints won’t have to play against Alonso on Sunday with revenge in the air…

PHOTOS: Liverpool unveil new 2018/19 kit

Getty Images
1 Comment

Liverpool have gone for a “pepper red” kit for the 2017/18 season.

[ LIVE: Stream every PL game ]

On Thursday the Anfield club released their new jersey for next season with New Balance once again their kit suppliers.

The key features of this new kit is a small collar, with a fresh white and red look throughout.

Check out the images and video below.