Wednesday, 26 April 2017

Reading Between the Lines

The 2016/17 regular Championship season is almost done and dusted.

With two games remaining for each team it is left to Leeds to attempt to gate crash the play off picture, most likely at the expense of Fulham and Blackburn to try to leapfrog out of the final relegation spot to the detriment of either Forest or Birmingham.

What seems highly likely and certain is that Reading (GD currently +1) and Huddersfield (+3) respectively will contest the playoffs for promotion to the Premier League.

Whilst Huddersfield's underlying ExpG stats have gradually gravitated towards their lofty league position, Jaap Stam's Reading remain an uncomfortable enigma for advanced stats.

Ben Mayhew, who runs the excellent EFL orientated site Experimental361 has consistently rated Reading as a lowly Championship team and Colin Trainor, one of the earliest analysts to develop the concept of ExpG has also tweeted about the Royals' apparent over achievement.

In addition, the ExpG model which powers Infogol's football app has Reading's underlying stats being consistent with a side in the lower third of the table, rather than striving for the pinnacle.

Here's the rolling six game, ExpG differentials for the still active protagonists at the top of the Championship to the start of April.

Wednesday, along with the two automatic promotion teams have been the most consistent ExpG teams this term.

Huddersfield, as already noted have gradually produced underlying stats that are fit for their position, while Leeds and Fulham have been inconsistent, but overall in credit.

The sole exception is Reading, whose underlying ExpG differentials have simply declined, even with a cut off point that omits a 7-1 thrashing at Norwich.

In terms of traditional goal difference stats, they share a similar figure with Derby and Preston, who have nearly 20 fewer points than high flying Reading.

If we look at Reading's ExpG figures, there is little to quibble about in their goal scoring exploits. Their actual goal tally agrees almost exactly with the modelled ExpG values from each goal attempt they have created.

The disconnect is on the defensive side of the ball.

Reading's Exp GD is -13, which would place them in and around the likes of Burton, and still relegation sensitive Forest and QPR. So they have over achieved on the defensive side of the ball.

If you run simulations on all of the attempts Reading have allowed their opponents in this season's Championship, they concede their actual total or fewer around 5% of the time.

The chances of Reading doing as well, defensively, given the volume and quality of chances they have conceded is relatively small, but the chances that someone over achieved by as much as the Royals at sometime in the recent past or even just this season becomes more likely.

While defence is a group activity, much of the burden falls on the keeper, in Reading's case, the veteran Omani, Ali Al-Habsi.

We may use an alternative ExpG model for keepers, which focuses merely on shots on target and incorporates post shot information, such as placement. power, swerve or deflections to help us understand if the keeper is playing above the save expectations of such a model.

As with the general ExpG allowed model, Al-Habsi has also over performed. It is again around 5% that an average keeper does as well or better faced with the shots Reading's keeper has been required to deal with.

The goodness of fit of this attempts on target model can also be tested to see if Al-Habsi is coming close "breaking" the modelled ExpG or if we can speculate that he has been somewhat lucky.

If we rank the efforts faced by Al-Habsi in terms of difficulty, he has had a particular purple patch when dealing with moderately difficult attempts. He's conceded just 8 goals from chances that were ranked as being between a 55% chance and 80% chance of being scored, compared to an expectation of over 12 goals.

However, over the entire range of chance probabilities he's faced the deviation from the model has around a 15% chance of having occurred by chance.

In short, he's saved more of the chances that the model expected him to save and he's progressive, if slightly unevenly, let in more of the most difficult shots.

A 29 year old Ali Al-Habsi, six years from his peak?

Overall, Reading don't break a variety of ExpG models, even on defence and while luck is the most likely explanation for their over performance, I wouldn't be so presumptuous as to assume skill differentials or tactical nuances aren't entirely absent.

However, even if we allow an Al-Habsi inspired Reading a near equal GD, that explains why they aren't actually in the bottom third, it still remains puzzling as to why they aren't drifting aimlessly in mid table with Derby and Preston.

Newcastle are the poster child for out performing their actual GD, claiming around 10 more points than their single figure GD merited in 2011/12.

They share with Reading an imbalance of narrow wins with a handful of wide margin defeats scattered throughout the season.

Reading has won 16 games by a single goal margin accounting for nearly 60% of their current total points.

This may hint a the near mythical ability to "score when we want" as most exemplified by Manchester United, under SAF, Jaap Stam's former employer, but United perhaps aside, this ability is often difficult to maintain.

The effect is more striking in the Premier League, but a side which relies on single goal wins for a large bulk of their points sees their points total decline by around 6% in the subsequent season. Maybe implying their record was more down to unsustainable influences.

Reading have also profited from late goals. As a crude measure, 11 extra points have been won from goals scored after the 87th minute. Another alchemical trait practised almost exclusively in the longish term by SAF

It would be churlish to brand Reading as merely fate's flavour of the season, but it would equally be unwise to take their current lofty league position entirely at face value.

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