Why Possession Value Is Bollocks

Expected goals. Expected assists. Expected passes.

How likely is a shot from here to be a goal? How likely will a pass from here to there turn into a goal if the guy receiving the ball shoots? How likely will a pass from here to there be successful?

All models have flaws and these guys are no exception. But they all have one thing in common.

They pretty much work as intended.

Why?

Because they are fairly simple by design.

They are fairly simple by design because they are singular actions.

On top of this, 99 times out of 100 we can be sure of a player’s intention when making the play or in the case of expected assists, infer it afterwards because a shot happened regardless of the initial intention.

We know what we are trying to measure here, and its not difficult to do if we have the data.

The trouble is, these models are a bit boring now.

The new guy on the block in Analytics Town is the Possession Value type metric. Our chums at Opta define the idea thusly:

– OptaPro’s Possession Value (PV) framework establishes the probability of a team scoring from an individual possession.

– The framework assigns credit to individual players based on positive and negative contributions, covering key on-the-ball events.

Does it work?

When looking at preliminary results, we noticed a major negative influence on the scores for players who are often involved in attacking plays.

We believe it is crucial to assign blame and/or credit only where it’s due. Therefore, in our framework, the punishment for the loss of value of the possession is capped at 0.025 (the average value of a possession).

That’ll be a no.

I am not against the idea of expanding analytics into more exciting, more complex football actions. But let’s build on solid foundations.

Let’s look at the idea itself again:

– OptaPro’s Possession Value (PV) framework establishes the probability of a team scoring from an individual possession.

Is this fairly simple by design? Well, the actions are no longer singular, multiple actions take place in a possession.

Where does a possession begin and end? Up for debate. Where does the following Everton possession end from the initial kick off v Brighton yesterday?

Is it when Djibril Sidibe’s launch down the touchline gets cut out by Dan Burn? If so, does Alex Iwobi’s touch that finds Bernard start a new possession? Or does no team really have the ball under control here and it’s a possession for neither?

My view is that the whole passage is Everton’s possession until about 18-19 seconds when Brighton (to me) gain full control of the ball back. I’m sure some of you will disagree. I know for sure that the main data suppliers all do.

Immediately we have problems with definitions of what a possession actually is.

– OptaPro’s Possession Value (PV) framework establishes the probability of a team scoring from an individual possession.

Is the intent of every possession to score a goal? If not, then why are we measuring all possessions against it? How many players in the clip are thinking: “If I do this, we’re more likely to score.”?

What’s the actual thought process from the Everton players there? Is it more like: “Ooh fuck, I’m under pressure here, let’s just keep it and if it’s too risky we’ll send it long, so if we lose the ball further up the pitch, there’s less danger”?

If it is then what’s the point of measuring it against the probability of scoring?

At each stage of a possession, the intent in moving the ball is different. It can move from retention, to advancement, to retreat to deliberately giving the ball away in a less dangerous area.

Possessions are a building block to get from A to B to C to D etc on the pitch and then create openings for goal opportunity.

So measure them in separate blocks.

Measure attackers v each other in the final third.

Measure centre backs on ball advancement to the next thirds of the pitch.

Measure midfielders on how brave they are in not going backwards all the time to alleviate pressure.

A goal may be the ultimate team goal, but it is not the ultimate goal of every player. Stop creating models that pretend it is. Possessing one has no value.

 

 

 

 

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The Everton Diary Game Week 9 – Whittling Down the Shortlist

In the last piece I eliminated managers from the top 5 European leagues using my pressing metric. Today, the humble xG metric gets its chance to whittle down the candidates. Let’s go.

Eddie Howe. Bournemouth finished last year with -7xGD, with the same attacking output As Everton but a much worse defensive performance. Despite being an extremely hard-working side and one that likes to press, Howe has never got his defence tight in the Premier League. His Bournemouth side continuously leaks shots and look vulnerable. It’s the same story on the underlying numbers every season. Me? I’d pass because of this glaring weakness that Howe refuses to address.

Jose Luis Mendilibar. Eibar smashed up La Liga in the xG stakes last year finishing second only to Barcelona with an impressive xGD of 19. In reality, however, they finished only 12th, which immediately raises two questions. Firstly: ‘If he had the players to play this system how good could he get a team to be’. Alternatively: ‘This xG lark is a load of old bollocks, innit?’

That 12th place finish was one of the biggest underperformances I’ve seen in top league numbers. Eibar were 5th in my xG numbers the season before, and 8th before that. Each time with a positive xGD. Each time under Mendilibar. Both times they finished top 10 in reality.

Mendilibar spoke last year of learning English well enough to come and manage here. Eibar is a small town club with a small town budget that has played lower tier football until this decade. Mendilibar would definitely be on my shortlist.

Adi Hutter. Eintracht finished last season 8th in my xGD table (on -1xGD) for Bundesliga but 7th in reality. Pretty decent in attack on the numbers and ok in defence, Hutter’s side smashed it on both sides, scoring more than xG suggested and conceding less than it suggested it should too. I have no other underlying data for Hutter but won league titles with RB Salzburg and Young Boys since 2015 (and several times in Austira before that). Eintracht are going well again both on the numbers and in reality this season. Hutter definitely goes on the shortlist, although I can’t find a video of the man speaking English.

Bruno Labaddia. After a couple of years out of the management game, Labaddia returned to football as manager of Wolfsburg last year. A traditionally well-funded outfit, they finished 6th in my Bundesliga xG table and 6th in reality. They’re going ok again this season and are about as good as Eintracht over the last 12 months or so. Labaddia has had several decent sized clubs in Germany but never massively achieved. Not for me, Clive.

Both Pal Dardai and Sandro Schwarz don’t do anything for me in the xG takes. Bottom half there, bottom half finishes for Hertha and Mainz respectively over the last few years. Nothing sticks out as being particularly special about their teams. Pass.

Walter Mazzarri. Middling xG numbers last year for Torino. Fairly poor attack, ok defensively, but smashed xGA against in reality conceding a whopping 13-14 goals less than expected. Poor numbers at Watford, especially on the attack front. We’ve had enough of bad attacking thanks. But no thanks.

Gian Piero Gasperini. Atalanta have been a top 3 xGD team in Serie A for the last two seasons. Good offensively which is what we’re all desperate for at Everton. The best manager here on that score so far doing enough to get around 70 xGF in both those seasons. Tough gig in the Champions League so far this year and not looking likely to advance from the group makes it slightly more possible that he’d actually come. If you don’t ask you don’t get. Again, I can’t find an interview with him in English, but haven’t looked that hard.

Claudio Ranieri. Well we know he speaks dilly ding dilly dong so we’re ok on that score. Solid season with Roma last season on the xG front. Good attacking numbers let down by conceding plenty of chances too. Lasted 5 minutes at Fulham and completely unable to turn them round after Jokanovic’s exit last year. Looking for his fourth club already since taking Leicester to the title. His CV has some huge clubs on it and is not to be completely sniffed at. He’s also available.

Luciano Spalletti. Two very good seasons of xGD with Inter since 2017 having finished 2nd in his season back at Roma in 2016-17. I have to admit, I loved this guy in his first spell at Roma but he’s always fallen slightly short since. I have seen it said that Spalletti was the ‘inventor’ of 4-2-3-1 so he’d fit right in at Goodison straight away even if he doesn’t appear to speak the Queens’. And he’s also available.

Stefano Pioli. Solid if unspectacular xG numbers with Fiorentina the last two seasons and not as good as the underlying numbers of Gasperini or Spalletti. Again, doesn’t appear to speak English but he’s a lot younger than those two while still having big clubs on his CV and he’s available. That said, he’s never won anything. So he’s not going on my list.

Rudi Garcia. Ok xGD numbers at Marseille in two of the last three seasons (and one good xGD season) but the numbers suggest he’s not an attacking, aggressive manager hunting for wins. So he’s not going on my list either.

The last two guys picked up on from France, Christophe Pelissier and Alain Casanova are non-starters realistically and their names will not wash with fans.

Right then.

My final shortlist of potential managerial hires from the top 5 European Leagues having used just two metrics – one for the high press, one for xG leaves the shortlist pretty short:

Jose Luis Mendilibar, Adi Hutter, Gian Piero Gasperini, Claudio Ranieri and Luciano Spalletti. Only one with Premier League experience (and a title under his belt) but he’s probably the one you wouldn’t want because of familiarity and ageism.

Gasperini and Spalletti may think they’re out of our league (with some justification).

Mendilibar would be fairly bonkers and left field but he truly is pioneering an entirely different style of play in La Liga.

That leaves us with Hutter. The youngest of this crew, a serial winner so far albeit in lesser leagues and perhaps importantly, he’d likely jump at the chance to move to Everton to test himself against the greatest managers of the day knowing he’d get backed with some money.

Jurgen a Red. Adolf a Blue. Both in the same city? Even Stan Boardman couldn’t make that up.

It’ll be interesting to see who will be on Everton’s actual shortlist should Silva go. Do you think there’ll be any overlap?

 

 

 

 

 

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