Month: July 2016

What a difference three years makes.  Starting as a place to simply host good stats writing, the site still does that, but has become possibly the most respected place for football analytics on the internet. That’s not hype, it’s just truth. There isn’t anywhere else like StatsBomb. One of the things that makes the site different is we don’t publish data, we do analysis of the game. Often painstakingly detailed work that is unflinching in the level of reader it requires. It’s not Popalytics or bullshit infographics (okay, mostly not) - it’s always quality work. Articles published on the site are good enough to be used by professional clubs, while still hopefully being fun and readable enough for a widespread audience. If you had the real names of all the followers to our Twitter account, you’d find an awesome collection of smart people working in and around professional football who follow the site. Teams initially intrigued by many of the ideas published here have now copied them and made them their own. Professional football clubs have also hired a number of contributors for jobs over the last three years, which might be the thing I’m most proud of. Giving people a chance to live their dream of working in football is pretty special, as I know from personal experience. It’s not just football StatsBomb has affected, it’s also the media. Back when we started, non-penalty goals were not a thing. To my knowledge, Per 90s didn’t exist anywhere outside of a rare Opta piece. We wrote about better ways to analyse the game while learning to do so ourselves, the public responded, the data sites made changes, and the media ever-so-slowly followed suit. First a thank you to all the writers that have contributed over the years, without you the site obviously would not exist. We have never monetized the site because if we tried, our use of data would suddenly become very complicated, and honestly there are few effective ways of monetizing websites now that work . Guys who write here do it for free. They do it because they want to challenge themselves and ideas about football in ways almost no one else does in public. So many man hours have been spent gathering and studying data prior to writing anything on this site, it’s impossible to consider what is produced here as anything other than a labour of love. Except, very occasionally, when they are an equally motivated labour of hate. Also thank you to the fans that have helped us out, especially with technical insight and programming work over the years. A very special thank you to James Yorke, without whom the site probably would have died when Colin Trainor and I disappeared inside of clubs. James's work makes me very happy I left the site and all the work up when I was hired, which often didn't happen in other sports when people went professional. Finally, a thank you to all of you readers, whether you were there at the beginning, or have just become a fan of the site in recent times. There would be almost no point doing any of this without people who were excited to engage with the material. Further Thoughts The world is different now than when I started the site three years ago. I feel like we used to get a lot more social media shares from bigger accounts that would push us along. Those accounts were rewarding quality work with wider publicity. For some reason that seems to happen a lot less often now, and I don’t know how to change it. In terms of audience, our Twitter followings have grown immensely over the years, but the actual average readership for an article has not. Maybe that’s a problem with the choice of material – I was writing a lot about transfer prospects back in summer of 2014 before it became my actual job, and I’m a bit more reticent to give that away now, so that clearly has an effect. But maybe we just stopped growing at some point and neither James nor I am aware of what to do to plug us back into the machine while not sacrificing quality of content for hits. Some work on the site will always appeal to a niche audience, but it would be nice if our trending suggested we were consistently less niche than before. In most cases, the only thing anybody gets from publishing here are kudos and maybe a touch of popularity. If you like someone’s work, tell them, but also nudge it along to other interested parties if you can. Post A LINK to Reddit, or to the Football365 forum, or some other high traffic venue that brings people to the site. DO NOT, if you can help it, post whole swathes of articles to anywhere because that traffic never hits us. Less traffic = less impetus to write = less content = eventual death of the site because what’s the point? It costs you nothing to read us. If you like the content, please give back in whatever way you can. I was also entirely sincere in the podcast today about wanting to hear from people in what they'd like to see more of from the site. No ideas are bad ideas, and after 3 years, maybe some of your ideas will add a new impetus to material for the coming season. All the best, Ted Knutson Owner, StatsBomb.com July 15, 2016 mixedknuts@gmail.com @mixedknuts   Postscript - Honest Personal Stuff Working in football is an addictive drug. It’s especially so when you think that you have an edge, and believe you can dramatically improve whatever club you work for. Right or wrong, that’s where I am at right now. Those of you who follow me on Twitter can probably sense my frustration recently at the fact that I don’t have a club to work with this season. This is especially painful when I see mistake after mistake in the transfer market fly by on my Twitter feed. It sounds arrogant to put it in writing, but at this point it’s based on years of hard work and data: I am literally one of the world’s experts at using statistics in football, and especially in recruitment. With my skillset, I can

• Find a club better players.
• Make a club money in the transfer market.
• Create actual goals on the pitch via tactical improvements including something I have avoided talking about much at all, but had amazing success with at Midtjylland: SET PIECES.

How much is a single goal worth in the Premier League? In the right environment, my approach can generate lots of them. Sadly, I am once again on the outside looking in. The problem is that football is football, and it takes someone pretty special to trust the word of a relative outsider that things can be done better in almost every club in the world, across the board. You see, football is a traditional industry. The way things have been done is generally assumed to be the best way, often with little critical thought being given to WHY this belief exists or whether it is even correct. Knowledge is passed down from master to apprentice, again often without reflection on whether it’s the best way – it’s simply the way they know how. What we've learned about traditional industries over the last 30 years is that they are incredibly ripe for disruption. Add data and technology to traditional industry and BOOM, you suddenly have something much more efficient and effective than before. In certain cases, basic disruption creates wildly unexpected positive benefits the traditional approach never imagined. Football is in that spot right now. But in order for that to happen, people at the top have to first be convinced the problems exist. Then they have to realize traditional football gurus are unlikely to know how to solve these issues, and often don't notice the issues exist in the first place. And finally, people with solutions need to be empowered to make change. This isn't an "advisory capacity" approach. It requires decision making power and ability that is rarely seen on the football side of clubs. From my experience this summer, it still feels like the football world is a long way from being ready to do that, even with strong evidence backing up the arguments. The issue isn't isolated to football - we're still seeing it crop up constantly in hockey, and we saw it for ages in baseball until eventually everyone basically admitted the stats and technologists were right too damned often to ignore any more. NBA was probably the sport that modernized the fastest, but even there you still see media dinosaurs peddling the same old wrong information, week in and week out - information that is often directly refuted by the actual data and decision making from the front offices themselves. In modern media, the universal rule is: Talking heads gonna talk. TV requires content, and a bit like politics, you can lie all you want as long as you get a reaction. Combine all of this with the feeling I’ve had recently that any innovations you release to the public are simply going to be copied and iterated by others in no time at all, with little or no credit going back to the person who did the hard work, and it’s a bit of a downer. Original thinking and innovation take a tremendous amount of effort before you can achieve results. Seeing that immediately copied and spun into the ether makes me question what the fucking point of innovating is in the first place. I’m on holiday the next two weeks and will take some time away from the site and football and see if my mood lightens. Maybe a grumpy disposition is causing me to misread the signs, and that the football world is ready to evolve and improve. My worry - based on my own experience and that of plenty of others - is that even after three years of hard work and a lot of success both on and off the pitch, we’ve barely moved the needle at all. There are only so many times you can stubbornly bang your head against a wall before you start to ask yourself whether that’s a healthy thing to do in the first place.  

End of my Hiatus

First things first.  Although I never publicly announced it at the time, I’ve spent the last 12 months consulting for a Premier League football team.  My engagement ended at the end of the 2015/16 season and so now I’m able to pick up my virtual pen and begin writing again.  It’s been about 18 months since I’ve done this so please be gentle...

Player Aging

Player aging is a thing.  We know that people get physically stronger as they mature from a teenager into an adult and then some time later they begin to lose some of their physical edge.  That much is a fact, but what is open to some debate is when exactly those transitions happen, what is the extent of the improvement and subsequent decline and also whether players’ increasing tactical knowledge and “game sense” as they gain experience can help offset some of their loss in physical edge.

There have been other pieces written on player aging.  Michael Caley has written about this, as he has done with just about everything else to do with football analytics, but while most of the current writings tend to focus on the share of player minutes at each age I wanted to have a more detailed look at how some individual components of players’ performances are impacted as they age.

Data Rules and Explanations

As always, Opta is the source of the data that I’m using in this study and I’m looking at the Big 5 Leagues for the 6 seasons from 2010/11 to 2015/16.  I wanted to take a look at each position separately as the skills required for each position may be different.

I used the Opta starting formational information and included players who started the games, dividing them into the following positions:

• Full Backs
• Centre Backs
• Midfielders (Central: defensive or attacking)
• Wingers
• Forwards

I undertook the analysis at a game by game level, so in the games where, for example, Christian Eriksen started centrally his numbers went into the Midfielder grouping, whereas when he played on the left side of midfield his numbers went into the Wingers grouping.  There may be an amount of arbitrary decision making around the position assigned to the players by Opta, but I think my method should ensure that players are broadly assigned to the correct positional grouping.

I then excluded any players that didn’t play at least 540 minutes in a given position and analysed the remaining players through the use of a few summary season metrics.  The hope is that we get an idea of how the individual components of a player’s game are impacted by their aging.

I grouped all players together who were younger than 20 (identified in the “Teen” group in the charts below) and at the other end of the scale I grouped all players that were older than 32 in the “Old” group.  At my stage in life, 32 actually seems quite young, but that’s probably a discussion for another day!

The player’s age for each season is taken as his age as at the 31^st December in the season, and the individual metric value generated for each age group is the median value of its population. As there will likely be some variation across leagues I initially analysed each of the five leagues separately, but there was quite a bit of noise as some of the bins were too small so I decided to combine all the leagues to maximise my data size as I want to be able to identify the general trends.

In this first part of my look at Player Aging I will concentrate on the attacking positions, Wingers and Forwards.  Other positions should / may follow this article.

OK, so now on to the good stuff………

Wingers – Key Metrics

Let’s go straight in and look at the key attacking output of wingers; namely Open Play Shots, Open Play Key Passes (regardless of whether those KPs were converted or not) and Scoring Contribution.  Scoring Contribution is defined as Non-Penalty Goals and Assists, and as you are reading this on StatsBomb all three metrics are shown on a Per90 basis.

The secondary axis (the one on the right side of the chart) is the axis for Scoring Contribution, whilst the main axis displays the Shot and Key Pass numbers.

Open Play Shots

The red line represents Open Play Shots per 90 minutes and there is a very tiny increase in this level until players reach the age of 26 (1.95 at 26yo vs 1.85 at 22yo).  After the age of 26 there is a very clear drop off in shot volume for wingers and by the time they reach 29 years old their shot volume has dropped to about 1.6.  There is then a small uptick at 30, but the pattern is clear; Shot volume for wingers reduces after they reach 26 years old.

Open Play Key Passes

Immediately we can see that for the blue line (Open Play Key Passes) the change in output for wingers as they age is not as severe as that observed in their change in shooting volumes.  There is a slight increase from teenage years until players reach the age of 23, and then it flattens until 28 when it begins it’s very slow decline.

One hypothesis for this almost (but not quite) horizontal line is that there are many different ways to play a Key Pass, for example, they can be created through a burst of speed or through the playing of a well-timed, accurate pass.  The former of these methods is more likely to happen with younger players, whereas the latter may be suited to a more experienced player and so we don’t really see age having much of an impact on how creative wingers are.

Scoring Contribution

The green line, which represents Scoring Contribution, is the absolute key one in terms of final output for attacking players as it represents how many Non-Penalty goals they either score or directly assist.  The pattern here for wingers is very clear as it steadily increases from their teenage years until they reach 26, at which point it begins its steady decline.

In absolute terms, the median Scoring Contribution value for 21 year old wingers is 0.29 Per90, and this increases to 0.34 by the time they reach 26 years old, and then decreases to 0.28 by the time they reach 30.  Those differences may sound small, but over a 38 game season the difference in the output between one 26 year old and one 30 year old winger comes to almost 2.30 goals.

Forwards – Key Metrics

We’ll now run the same analysis for Forwards as we did for Wingers.

It’s probably no great surprise to see that the lines on the Forwards key output charts following similar patterns as those seen in the Wingers’ chart.  Shot volume increases until it peaks at 27 while Key Pass volume broadly remains fairly flat throughout the career of a forward.

In terms of the composite metric, the green Scoring Contribution one, there is an anomaly with 32 years and older forwards performing very well (notably in Italy). I assume there will be a large element of survivor bias in this number as any 32 year old (or older) that is playing is more likely be doing so because they are performing whereas the same probably can’t be said for the average 30 year old forward.  However, leaving this wrinkle aside we can see a general increase in Scoring Contribution for forwards until they reach 28 years of age, at which point their numbers can expect to decline.

The extent of the decrease in Scoring Contribution between a 28 year old forward and a 24 or a 30 year old forward is similar to what we seen when looking at wingers.  The median 28 year old clocks up 0.43 Scoring Contribution Per90, compared to 0.37 for both a 24 year old and a 30 year old.  This lack of a peak age forward leading the line for a team again equates to an expected shortfall of 2.30 goals over a full season.

Wingers - Other Metrics

Apart from the key output metrics I wanted to look at how a few other metrics reacted, across the population as a whole, depending on the age of the winger.

Dribbling

Two of the metrics on the above chart relate to dribbling.  The yellow line is the traditional Successful Dribbles stat as provided by Opta while the orange line is one of my processed metrics.  The orange line represents the number of metres that the player dribbles the ball closer to the goal than from where they picked it up; so this shows how much progress towards the goal the player makes when carrying the ball.

These two dribble metrics follow a very clear and similar pattern, albeit a somewhat surprising one.  On the whole, wingers will dribble the ball less with each passing year.  Unlike the shooting and Key Pass metrics that we read about earlier in this piece, players do not carry the ball further or more often in their mid to late twenties than they do in their younger years.

To me, this is really interesting.  We have seen that wingers’ attacking output (as defined by shots and assists) increase from their early twenties until they reach 26 years old yet we see that they are carrying the ball less often and over shorter distances.  The median winger will have 1.1 successful dribbles when they are 26 years old compared to 1.6 when they are 20 or 21 but their decreased ball carrying does not seem to have an adverse impact on ultimately how creative they are.

One hypothesis for this is that they simply become smarter footballers as they mature.  They make better choices as perhaps they no longer feel that they have to prove themselves by beating their man like they did when they first broke into the team.  Perhaps they learn to lift their head and look for better options instead of simply carrying the ball for its own sake.

The takeaway from this discovery: So while we look at (for example) a 19 year old Raheem Sterling and marvel at his numbers we should bear in mind that, whilst his end product should increase until he reaches his mid-twenties, we should expect his ball carrying numbers to reduce.

Fouls Won

The purple line displays the number of fouls won or drawn by the median winger at each age of his professional life.  Although the line looks fairly flat on this chart there is a slight consistent reduction in fouls won from 22 years old (from 1.8 to 1.45 by the time the winger reaches 30).  Despite the existence of this slight decrease in fouls won as the winger ages it’s clear that the pace of decline is nowhere near as sharp as that shown in the main dribble metrics.

Once again, that’s an interesting result.

Does this suggest that it demonstrates players becoming cuter or more “game smart” as they develop in years because they can draw a foul comparatively easier (when controlling for how much they carry the ball) than when they were younger?  Or does it mean that fast players can’t or don’t win free kicks as often as we think they should?

Non-Corner Crosses

The last remaining line on the chart, the black one, shows us how many non-corner crosses the median winger plays.  There is a blip at 25 that otherwise distorts a fairly clear increase in the number of crosses wingers play until they reach 27 to 29 years old, after which point the output sharply decreases.  As the value of a cross is pretty marginal I’ll not spend any more time on this one but just wanted to mention it as I pulled the data to get to this point.

Forwards – Other Metrics

No comment required here as the lines for the dribbling metrics and fouls won for forwards are almost a carbon copy of the wingers’ numbers produced earlier.  This in itself is encouraging as the emergence of similar patterns across two totally distinct data sets gives us confidence that there is signal in what we are looking at.

Conclusion

For most readers, this won’t be the first time they have read about Player Aging in football, and as a concept it is quite straightforward.  However, the reason that I undertook this research was that I was unable to quantify the impact that playing a 24 year old or a 30 year old player instead of a player at peak age (assuming both have achieved similar percentile achievements in their age bracket) for its position would have on a team’s expected output.

Balancing a squad from an age perspective is difficult; buying to improve your chances of immediate success will have a negative impact on your future chances and buying young talent to maximise resale value means that the team won’t be at their absolute peak for the forthcoming challenges.  It’s undoubtedly a tough line to walk successfully but now when teams make decisions around the age structure of their squad (here’s looking at you, Man City) we can be a little more knowledgeable around quantifying the potential impact of the decisions that are made.

Although the charts contained in this piece relate to the median number posted by each each group for each metric I also looked at the 80th percentile and, while the curves were obviously higher than the median ones, the drop off from the peak was roughly a similar amount to those displayed here.

Based on the data that I have analysed it looks like the peak age for a winger is 26, whereas a forward peaks a year or two later when they reach 27 or 28 and the expected impact of playing the 24 or 30 year old instead of your peak age player on an ongoing basis will shave approximately 2.30 goals from your attacking output over the course of a season.