Saturday 23 September 2017

30 Year old Messi is Likely in Decline.

'Tis the season for small sample sized hyperbole to be liberally launched on a expectant audience and the latest recipient of the "If he continues at this rate" award for unrealistic dreamland is none other than Lionel Messi.

While Ronaldo has been kicking his heels and the occasional Real Betis player, Messi has single-handedly (with the help of 10 teammates) launched Barcelona seven points clear of their perennial rivals from Madrid.

Messi turned 30 in the close season, he's playing in his 14th La Liga season and is undoubtedly one of the two best players of the last decade.

But he is still human and bound by the natural athletic decline that eventually sets in for every footballer.

Players improve with maturity and experience, peak, usually in their late twenties and then begin an inexorable decline, albeit from differing peaks.

Messi's post birthday, six game return in the UCL and La Liga, but discounting a two legged Spanish Super Cup defeat at the hands of Ronaldo's Madrid, has been spectacular, even by his standards.

It has spawned at least one article, liberally salted with stats to enhance credibility, eagerly anticipating the untold riches to come.

Unfortunately, five or six games is so small that you will inevitably get extremes of performance, either very good or very bad.

Particularly, if you selectively top and tail the games to eliminate a comprehensive defeat, devoid of any Messi goals from open play at the hands of your nearest rivals, but conclude with a three open play scoring performance from the Argentine.

Small samples are noisy, unbalanced and rarely definitively indicative of what will happen in the longer term or even just a single season.

Barcelona has played Alaves, Eibar, Getafe, Espanyol and Betis, only the latter is currently higher than 13th.

As a data point it is all but useless to project Messi's 2017/18 season.

Individual careers are statistically noisy. Injury, shifted positional play and team mate churn are just some of the factors that can make for an atypical seasonal return, even before we try to decide which metric is sufficiently robust to reflect individual performance.

If we use goals and assists to judge Messi up to his 30th birthday, his delta, the change in non penalty goals and assists per 90 from one season to the previous season trends negative when Messi was 27, guesstimating this was when he peaked.

If we include 2017/18's small sample sized explosion as a fully developed rate for this upcoming season, the trendline still becomes negative this year.

If we regress this current hot rate towards Messi's most recent deltas, as we should, Messi's peak stretches to his 28th birthday.

But by his own standards he has likely peaked.

Open play goals and expected goals for the last three and the first 5 games of 2017/18 tell a similar gentle decline, even allowing for Messi's recent spurt of scoring.

Actual, non penalty, open play goals/90 are trending downwards, as are Messi's xG per 90 on a 10 game rolling average.

The actual trendline is also probably more shallower because of the narrative driven choice of his three open play goal spree against Eibar providing the doorstop.

That Messi consistently over performs the average player xG isn't surprising, but the peaks, like the one he's currently enjoying is often driven by a glut of relegation threatened sides turning up in Barcelona's lumpy quality of schedule.

Enjoy the blips, but don't draw conclusions based on so little evidence.

Data from Infogolapp.

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