The Expected Goals Philosophy: A Game-Changing Way of Analysing Football

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Now the correlation for rank is improved to 89% and for points it is 83%. Please, remember that correlation is a nonlinear function. So an increase from 73% to 83% is quite a feat and shows that PSxG is informative whereas xG is not in this case. We don’t know exactly when it happened, but some time over the past 10 years the phrase “expected goals” (or “xG”) became a staple of the football dictionary. To this day, we’re not quite sure what it means. Now one criticism might be that the top 30 is too small. Although 30 sounds like a small sample size, 30 is often used as the minimal sample size . Sample size ought to reflect what we are looking for. When it comes to using xG for the recruitment of players, what clubs are looking for are players who can make a difference scoring wise. Preferably, clubs hire players who score a lot, but cost a little. Dalmau moved to Heracles transfer free. Clubs want players who score above average. Or in other words: clubs are looking for players who make it to the top 30! If they use xG to base their decision making on, they are going to make too many bad decisions. Circularity Soon, those who do not understand or pay attention to xG data will be left behind. The Expected Goals method allows you to speak about football in a more intelligent language.

Brentford fans will hope there is substance behind the above dead-ball theory, and it is clear that misses like Mbeumo’s last weekend are the exception rather than the norm. But the 68% correlation is misleading. Again, thanks to the work of Ashes, you can see that the 68% correlation is artificially inflated by combining the high correlation of low performing players, with the low correlation of high performing players. This issue has been discovered by Nassim Taleb in his criticism of IQ . What I have done with the help of Ashes, is apply the same principle to xG. Here are the results: I can't even figure out who could be a good audience for this book. An average fan, trying to dip his toe into advanced statistics? The book litters him with way too much numbers while teaching precious little. Someone, who is more interested in the depth of football and/or advanced statistics? The deepness of the actual coverage of xG here is extremely shallow, offers almost no insights on modeling, mathematical or any other level. I can't picture anyone who would like more than a third of this book.

Summary

I hope you like hearing about Arsène Wenger referencing xG in a post-match interview once, and Jeff Stelling going off on xG during a Soccer Saturday broadcast, because you’re about to hear about these incidents (amongst others) a LOT. But the xG value doesn’t (and I cannot emphasise this enough) tell the full story of a game and xG works very well in conjunction with other determining factors, but much less so as a standalone. The longest section of the book explores expected goals’ role in betting to date. Tippett describes how Smartodds produced their own expected goals model to identify value in betting markets and place money on teams that the model recognised as having a better chance of winning than the bookmakers’ odds suggested.

Even some of the negative reporting of xG has helped raise awareness. Jeff Stelling’s infamous rant would have introduced a lot of laymen to the concept of Expected Goals – those people might have then gone on to do their own research and end up liking the stat. To remind you: Ashes has looked at the top 5 leagues and the Russian league. Personally, I am more interested in the smaller leagues, especially the Eredivisie. And I am more interested in whether it helps to use xG in concrete player recruitment, especially in finding exceptional players. At my work at FBM we have found the striker Dalmau for Heracles. Not only did Dalmau become the #3 top scorer that season, we also predicted that he would be worth 1.75 million in transfer fee for Heracles the next year and Heracles did receive 1.7 million for Dalmau (700K transfer fee and Dessers, a striker valued at 1 million). The writing style is mundane and unexciting, and there are a few grammar errors and typos, one of which was so obvious it makes me think no one actually proof-read the book before publishing. Are you surprised by the popularity of the xG Philosophy account? In a recent episode of Laptop Gurus, Carragher revealed he had read the book.

So what\u2019s the book about?

The new approach relied on using the data to find undervalued players in the market. It was a massive success and helped Brentford achieve five successive top half finishes despite having one of the division’s smallest wage budgets and fanbases.