First of all, I had intended to have this up this past weekend and not on Thursday, my apologies.
Secondly, I hope you all went out and looked at the stat table that Matty put together. Some great accumulation of data and in a nice little format. Great information and some stuff that isn't readily available anywhere else. Consume this, stat heads.
This past weekend during our recording session we talked about possession. This has been discussed time, and time again by people much smarter than myself. I won't waste a lot of my own words except to kind of bring things together.
Get more (much more) after the jump
Graham MacAree, wrote a brilliant piece about Opta stats and how they specifically calculate possession as a whole. To save you a bit of time, the summation of the finding is that Opta, at the time, calculates possession as pass volume. Meaning if you take the entire amount of pass attempts over the 90' minutes and divide that against each of the sides pass attempts you would get the reported amount of "possession".
Richard Farely does a great summation on why that's bad.
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.
Now I say "at the time" because I attempted to do that tonight and my math was a bit off. So it's possible they also incorporate another statistic or something a long those lines. It's highly unlikely that they have gone towards a game clock as they still report in percentages.
Now it's fair to argue that the possession stat is meaningless, as Rui Xu (follow him on twitter, seriously, do it now) of Sporting Kansas City Performance and Statistical Analytics department thinks the following:
In general, I think they’re useless because they don’t contain any context. There is little-to-no correlation with points (if anything, there’s a slightly negative correlation in the MLS), and it doesn’t really tell you anything on a performance analysis level. Once you start adding context is when you’ll be able to draw some narratives. What is the possession percentage of the road team after they go up 1-0? What was it before? What is the possession percent of the home team when up 2-0 after the 80th minute? You still have to be very, very cautious though. - Numerology: How valuable is possession anyway?
But, it's countered very well by the Revolutions Timothy Crawford.
It’s hard to say exactly what possession necessarily does at this point. Barcelona out-possesses everyone, but they certainly dropped some points and big matches. There have been studies that have shown teams that win often lose the possession battle, but as my statistics classes taught me, correlation does not necessarily imply causation. No one is saying the way to win more matches is to never have the ball. It’s trying to find what part of possession is important, and then applying that to tactics.
Look, there is a mass amount of information that has basically flooded our ability to start analyzing the American version of "the beautiful game," and guess what, we're going to turn it into 1's and 0's because we're all a bunch of Yankee bastards. But as we do that there are going to be plenty of things that we don't know. I'm not sold that Possession is useless, but I can't think of exactly what is needed to make it "good" or what "good" it could produce at distant point in the future.
Matthias at a certain point on our podcast mentioned specific time spent in attack or in the opposing third, versus the ball residing in your own defensive third.These things of course matter as they will eventually create opportunities for you or your opponent. That leads into the thought that not every chance on goal is documented by a shot. There are plenty of these that stopped just short by defenders or goal keepers making last ditch efforts.
That being said if you sit inside and lob in crosses hoping to get lucky, Charles Reep style, against a team such as San Jose or Los Angeles that is remarkably well versed in protecting such an attack, what does it really matter how much time you had in the attack. You wasted it.
That being said, Zonal Marking has done some correlative work between the relation of shots and possessions.
As you might expect, there’s a fairly obvious correlation – the more possession you have, the more shots on goal you’re likely to attempt, which is hardly a revelation.
The graph is interesting, however, for two reasons. First, because there are clear differences between the five separate leagues. Second, because there’s a handful of sides that don’t fit the pattern, and a lot of variation amongst the sides who see a lot possession.
The sides who are significantly ‘higher’ on the graph compared to the line of best fit are particularly efficient with possession – they have more shots than you’d expect for the amount of the ball they enjoy. Those who are significantly ‘lower’ are less efficient – they see a lot of the ball but record relatively few shots on goal.
Of course, being more or less efficient is not necessarily ‘better’ – because the sole purpose of possession is not to score a goal. Possession can be used as a defensive tactic to play out time when a side is ahead, and can be used to tire the opposition, before attacking more directly later on. The intention here is not to ‘rank’ sides, but to show their different styles.
I think the biggest thing is how he ended those paragraphs "but to show their different styles". I think the biggest thing that possession shows me, at least for the time being, is what type of team you are. Are you comfortable with the ball or without it? Do you run up-and-down the pitch all day, winning and then losing possession; pressing for that additional chance at goal?
Maybe current possession stats can't tell us all of that information. But looking at break downs and heat maps of possession and the pitch, where players possessed the ball the most, can supply and relate to us an (albeit short) narrative. And ultimately it's all about context and applying it to the data that we use. Understanding why we chose the data we did and then being able to articulate it back to others, who can point out deficiencies as well as some of it's strengths.
I'll include one additional link here on the back end of this thought. The site Soccer By Numbers by one Chris Anderson, producer of the book "The Numbers Game", hosted a post last year by Andrew Brocker. It doesn't really have anything different than what you've likely seen other places, however, I feel compelled to include it.
Brocker creates a neat little chart that displays the relational values between successful passing and maintaining possession of the ball between national clubs during the 2012 Euros. There are some interesting thoughts that go along with it and a tidy summary. I encourage you all to take a look.
Again, this isn't about coming to a conclusion, it's about continuing the talk and the attempt to raise the level of knowledge and understanding on a specific topic. I don't have hardly any of this figured out and I'm sure that there are much smarter people out there that could contribute much more. Should you be them or find their material, make sure you point us in that direction.
Zones 1-6 have been broken down by Matthias previously, and correspond to the map displayed on the right. xGF is simply expected goals for, and AP% is simply attacking passing percentage.