James Grayson wrote a deliciously critical post today on the vain search for the best metrics to predict the likelihood of a single game result. He points to score effects in order to illustrate his point:
Score effects are easy to explain and impossible to ignore whilst watching a game once you know they exist. When one team has the lead then the onus is on the trailing team to take the requisite risks necessary to get into a goal scoring position. As the game wears on they are more willing to a) take more risks which leave them vulnerable defensively, and b) take shots from worse scoring positions. This combines to the losing team taking more shots, but from worse positions, than they would have done when the game was tied, whilst the team in the lead can bide their time and wait for better opportunities to present themselves, meaning they’ll take fewer shots than they would when the game was tied. Thus it makes sense that teams that get outshot still win a decent proportion of the games they play. And that’s the crux for me here – why does anyone care when there’s a damn good reason why they shouldn’t always correlate?
In other words, trying to isolate a metric beyond goals that will tell which side will likely win a single ninety minute match is a fool’s errand. Again, common sense, and again, let’s walk before we run.
What’s more interesting to me though is Grayson’s reliance on the work of hockey stats writer and Winnipeg Jets fan Gabe Desjardins to make his point. In fact, as hockey and soccer are sporting cousins to some degree, the work in the former has often influenced progress in the latter. PDO, now a vital component in understanding the influence of luck for most long-term team analyses, was ‘discovered’ by hockey writer Brian King.
As a Canadian soccer fan, this is intrinsically cool. But I think there’s also a lesson here, or indeed a warning, in working on single sport statistics in isolation.
— Ben Pugsley (@benjaminpugsley) February 26, 2013
One of the examples which I spoke to on the podcast yesterday was Cam Charron’s post on Backhand Shelf on media analysts misrepresenting certain single statistics to reach false conclusions (sound familiar?).
First, some immediate correlatives to soccer analytics jump out. Charron mentions ‘Fenwick Close,’ which is basically total shots ratio within a tied game state or single goal differential, thus correcting for score effects. So, you know, that’s pretty cool. But this is what really sang to my brain, in relation to some CBC HNIC analysts’ use of total blocked shots as a means to show that certain teams have more ‘grit’:
And that’s something Hockey Night in Canada will never mention, at least not with PJ Stock or Glenn Healy on the camera who constantly slam their fists talking about the importance of toughness. Teams that have the puck the most tend to the win the most games. All of the useful categories involve some way or another having control of the puck.
Look at the bottom of the chart. The correlation between road blocked shots or road goals against and home points is pretty high, only the correlation is negative. What that means is that the teams that give up the most goals and block the most shots are the ones who are losing games. I find this fascinating, that blocked shots can have such a negative affect on a team’s record.
Again, this isn’t wizardry. Think about this within an actual game and it makes complete sense. A team that is conceding goals will likely be conceding shots, and having to block more of them. Charron’s overall point though to the importance of puck control exactly correlates to Grayson’s argument to the purpose of TSR—teams that control the ball/puck in the final third will score more points over the long haul.
We’re not necessarily learning anything new here, but it helps underline the interest and importance of soccer analytics people looking into sister sports to better understand their own trade. It’s not coincidence that some of the best soccer analytics writers have repeatedly turned to hockey analytics work to improve their work, and that is not limited by geography (11tegen11, natch).
And as a hockey fan, that’s music to my ears…