Sunday 10 September 2017

Messi and Ronaldo. Expected Goals Makers, Takers or a Bit of Both.

With the increased availability of granular data, there has been a similar influx of advanced metrics, both for players and sides across a wider range of domestic leagues.

And while performance based numbers, often to a couple of decimal places, are the raw material for much of the analytically based content, their attractiveness and clarity of meaning rarely extend beyond the spreadsheet.

It therefore falls to visualisations to convey some of the rich seams of information available in such manipulated data sets in a clear and easily digestible format, such as Ted Knutson's  hugely popular radars.

Expected goals remain the flavour of the month, although BBC pundits are still immune, imploring players to "do better" with opportunities that are scored fewer than one time in 10.

A team or individual's attacking contribution can be neatly summarised by their expected goals and assists, standardised at least to a per 90 figure, with respect given to those who have achieved their numbers over a larger sample size compared to noisy small sample interlopers, ripe for regression.

Here's the xG/90 and xA/90 for the 70 largest cumulative, goal involvement achievers from La Liga's 2016/17 season.

Data is from @InfogolApp and has been restricted to open play chances and assists.

Messi and Ronaldo are among a clutch of players who have broken away from the main body of the plot, although they are also quite a distance remove from each other.

Messi was involved in around 0.85 xg+xA per 90 and Ronaldo around 0.65.

However, the former, while slightly under-performing against the latter in getting on the end of xG scoring chances, more than compensated by creating over double the amount of expected assists per 90.

So a simple scatter plot can begin to reveal fundamental differences between even the most high profile of players.

More information can be extracted by simply running a straight line between a particular player's point on a scatter graph and the origin.

Moving down such a line, you'll encounter players who in the season under scrutiny, achieved ratios for xg and xA that closely resemble those of the line owning player.

The magnitude of their cumulative performance is less than those players that are further away from the origin, but their shot/assist characteristics will be consistent with any near neighbours.

Messi was a more sharing team mate in open play in 2016/17, whereas Ronaldo headed the line of takers, rather than makers.

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