Tuesday, 5 September 2017

Premier League Defensive Profiles.

Heat maps and the like have been around for ages as a way of visualising the sphere of a particular players influence.

However, it's always nice to have some numerical input to work with, so I've used the Opta event data that powers InfoGol's xG and in running app to develop metrics that describe how teams and individuals contribute over a season.

Defensive metrics have lagged well behind goals and assists, so I looked at that neglected side of the ball.

Unlike goal attempts, counting defensive stats tends to be a fairly futile exercise. No one willingly wants to keep making last ditch tackles and racking up ever higher defensive events is more often the sign of a team in trouble.

There's also the disparity in possession time which gives the possession poor team more chances to accrue defensive events.

Therefore, pitch position, rather than bulk events seems an obvious alternative.

Allowing a side lots of touches deep in your territory is intuitively a bad idea and the higher up the field a side is willing or able to engage their opponent would appear preferable.

Measurements have been calculated from the Opta X, Y point of an event to the centre of a team's own goal line.

Thus a tackle or clearance made on the half way line will be further from this point of reference if it is made near the touchline compared to if it completed on the centre spot.

This allows for defensive event profiles for both a team and also their opponents.

A quick eye test appears to show that the more successful Premier League teams do their defending further away from their own goal than the lesser sides are either willing or able to do.

That the idea that doing defensive stuff higher up the pitch is the product of a good team is further developed by plotting where a side defends on average and where they allow their opponents to defend, again on average.

The relegated teams from 2016/17 mostly suffered the doubly whammy of choosing or having to defend an average of around 34 yards from the centre of their own goal line compared to nearly 40 yards for some of the top 6 and they also allowed their opponents the luxury of making defensive actions around 38 yards from their own goal line.

Notably Pulis again muscles into an area apparently reserved for relegation fodder with his defensive voodoo.

At a player level it's a trivial problem to find the average pitch position where he makes a defensive action and then find how closely or far flung each individual action is from this average point.

These numbers can then be used as the average position for a player's defensive contribution, measured from the centre of his own goal and also how widely this area extends to.

N'Golo Kante's an obvious candidate to see if this simple exercise again passes the eye test.

In 2016/17 the average pitch position for Kante's defensive actions was 45 yards from his own goal.

The average distance between this average position and all the defensive actions he made was 23 yards

The latter was greater than the average for all defensive midfielders as a group.

We could perhaps say that Kante was relatively advanced in his defensive actions (he was seven yards further up field that his former team mate Nemanja Matic) and his field of influence was also more expansive compared again to Matic and his peers.

Charlie Adam, by contrast appears more constrained by the role required from him. In 2016/17 he tackled deeper than both Kante and Matic and strayed less far afield.

He more resembled a disciplined central defender in his defensive foraging and in doing so remained roughly where his energy bar lands on the pitch around the 70th minute.

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