Friday, 21 July 2017

Shots, Blocks And Game State

In this post I described a way to quantify game state by reference to how well or badly a side was doing in relation to their pregame expectations.

So rather than simply using the current scoreline to define game state, it gave a much more nuanced description of the state of the game, particularly in those frequent phases of a match when the sides were level.

It also incorporates time remaining into the calculation. 

A team level after 10 minutes might be in a very different situation compared to the same score differential, but with ten minutes remaining. How they and their opponents played out the subsequent time may be very different in the two scenarios.

At a simplistic level, those teams in a happy place may be more content to prioritise actions that maintain the status quo, such as defend more, while those who'd wish to alter the state of the game might put more resources into attack than had previously been the case.

It seems logical that a more defensive approach should result that team accumulating more products of a packed defence, such as blocked shots, while any chances they do create may be meet with increasingly fewer defenders.

I took at look at the correlation between blocks and clear cut or so called big chances and the prevailing state of the game and there was a significant relationship between them.

A side in a poor state of the game had more chance of their goal attempts being blocked and his increased as their game state deteriorated.

Similarly, a side in a positive state of the game was more likely to create a chance that was deemed a big chance.

This appears to fit which the hypothesis of content teams packing their defence more, and increasing the likelihood that they block an attempt and if they do scoot off upfield, they're more likely to be met with a depleted defence.

However, correlation doesn't prove causation etc etc. 

In the case of a side being more likely to create big chances, there may be a confounding factor that is causing both the good state of the game and the big chances. (Think raincoats, wet pavements and weather).

That factor is possibly team quality.

The top six account for 30% of the Premier League, but took 48% of the wins, 43% of the goals scored and 45% of the league points won.

They're a league within a league, more likely to be in a very good game state and they also accounted for 43% of the league's big chances.

Team quality may be the causative agent for a good game state and for creating big chances, which correlates the two without either being causative agents of the other.

So I stripped out all games involving the big six to get a more closely matched initial contest, but the correlation persisted.

Teams in a good place against sides of similar core abilities were more likely to create very good chances and more likely to find defensive bodies to block the anticipated  onslaught from their opponents.

As a tentative conclusion, intuitive events that you might expect to be more likely to occur as strategies subtly alter do appear to be identifiable in the data.

Data from InfoGolApp

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