Saturday, 15 October 2016

Once Upon a Time in the Midlands

Time was when an international break simply meant a manager spending an anxious couple of days waiting for injury reports to materialise and trying to keep the left behind players amused.

Now it seems to have become the prime firing time and just under half of the 2016/17 casualties from the four top English leagues have departed during the current hiatus.

Two of the higher profile dismissals have come across the east/west Midlands divide, with RdM being stood down for Steve Bruce at Villa and Steve McClaren reacquainting himself with Derby at the expense of Nigel Pearson.

Both sides are currently treading water just above the drop zone, respectively in 20th and 21st position and it's difficult not to speculate that current league position has played at least as big a part in the managerial changes as has a fear of drones.

Using drones may take spying on your employees to new heights, but it is equally questionable as to whether the league table ever gives a true representation of a team's true worth or if it is indeed the table of (in)justice.

Beware of Low Flying Drones.
Both Derby and Villa have a negative goal differential after 11 matches, but this isn't reflected in their respective expected goals figures for all the chances created in their games.

Derby's return of six goals is a poor one for a side that has created chances worth nearly twice that and the randomness that is inherent in short runs of matches has been less than kind to Villa, particularly in how it has bestowed goals in games and regularly turned three points into one late in their matches.

An extra couple of points this early in the season can easily turn anxious glances looking downwards into optimistic ones looking upwards to better things.

Both Derby and Villa are in the top half of the table when measured in terms of the underlying performance indicators that tend to persist amongst the ebb and flow of randomness that sometimes predominates, getting managers sacked or manager of the month awards, dependent upon whim.

Longer term, weighted expected goals performances smile even more on Derby, regular play off contenders, who are ranked around the top six in the current crop of Championship teams.

While Villa, despite giving the 2007/08 Derby vintage a run for their money with an abject defence of their Premier League life last season, still remain a top half Championship ranked side.

Final league projections at their most optimistic propel Villa to the fringes on playoff football, even without fully accounting for the potential impact of their new crop of expensive attacking talent, a relative luxury Bruce has never had before. And Derby fare even better, even with their miserly actual points return through 11 matches.

Fan reaction to the appointments is cautiously optimistic.

Derby fans in particular citing McClaren's ability to "improve a player", the unwelcome distraction of Newcastle potentially calling during his first stint and the example from the Stoke end of the A50 of returning managers taking their team to the top flight.

Should the fortunes of these two Midlands sides improve, this wishful impact of managerial change will appear to materialise, but it will be scant consolation to the replaced duo that the underlying figures were largely in place and the table may have become merely a tad less untrustworthy in their absence.

Saturday, 8 October 2016

Expected Goals Distribution in the Championship.

Everyone is familiar by now with the concept of expected goals.

The challenge is to present team figures in a way that demonstrates the granular nuances that are often lost by merely quoting totals or differentials.

It has also been accepted that how a sides expected goals is spread over their chances also impacts on the results they achieve. A side that takes lots of low quality shots compared to fewer, better quality opportunities is trading the chances of  an occasional headline grabbing goal glut for a more regular diet of lower scores.

The latter being preferable in a low scoring sport such as football.

A cumulative expected goals figure lacks granular data, while a full blown, chance by chance simulation reveals more, but is time consuming unless automated.

A decent halfway house is to plot the expected goals figures for each non penalty chance created and faced by a side over the season to date.

Scaled appropriately, the fatness of the left hand side of the plot shows the level of high quality chances a team has faced or made, while the length of the x axis illustrates chance volume.

Here's Newcastle, 11 games into their Championship season, out chancing their opponents with a long x axis and bulking up on good quality chances, while denying opponents the same luxury.

The highest quality non penalty chance they have conceded has a goal expectation of just over 0.4.

It's less rosy over 11 matches for fellow relegated side, Norwich who have allowed opponents a decent number of good quality chances and leaders Huddersfield currently profile more like a mid table team, such as Wolves.

At the bottom, Rotherham are currently being swamped by shot volume of fairly high quality, while offering little in return.

Friday, 30 September 2016

The Biggest Liar in Football.

In a week during which many fresh contenders emerged, the league table remains one of the least trustworthy sources in football.

2-0 leads being the "most dangerous in football" made a welcome reappearance courtesy of James Richardson on the BT European Goals Show and was warmly greeted by the assembled hacks, but "the table never lies" still reigns supreme.

Small sample size, luck laden outcomes, random variation, strength of schedule, red cards, injury counts, new improved/useless players and managers, dodgy, but well intentioned interpretation of the laws, patchily applied, all conspire to produce a transient ranking that broadly sifts the very best from the very worst, but rarely manages to fully reward the bulk of closely matched sides with their just deserts.

Reinterpreting the mass of shots, saves and passes into a better reflection of the past and a less knee jerk projection of the future can be done by simulation of past and future games to generate the now familiar heat maps. These show the range of points a side might have/may well accumulate and the range of potential positions occupied.

This approach admirably illustrates the probabilistic breadth of outcomes that can befall a side given their core achievements, but nothing beats the implied certainty of a singular league position, with as much of the unsustainable luck stripped away.

The backbone of the table above, produced by Tom @UTVilla is the current position occupied by the team in the Premier League.

The expected position to the left is the most likely position occupied by each side based on an expected goals simulation of each match played in the season to date. So Hull are flattered somewhat by their current position, while Stoke should perhaps be a couple of places higher.

The right hand axis uses the actual number of points, ill gotten or otherwise and adds the simulated outcome of each team's remaining fixtures based on their core statistical achievements over the recent past. It includes the season to date, but not exclusively so.

This forecast position grants teams the luck they have enjoyed or endured to date, but denies them the extremes in the up coming months.

Tom's tube map to each side's ultimate potential May destination brilliantly illustrates the likely upwardly mobile or downward spiralling trajectories which may await...except possibly for Pep's Manchester City revolution.

The more mature Championship table, with four more sides compared to the Premier League and six new entries each season perhaps offers a more interesting chart and La Liga completes this initial trio of leagues.