Saturday 30 March 2013

Manchester United's Untapped Potential.

If Manchester United continue to score goals at their current average rate, they will finish the season with 90 goals, their highest total since 1999/00 when they claimed 97. It will also be their second highest in their Premiership history, including the two seasons when a 22 team Premiership each played 42 matches.

Equally, if we scale up their projected number of goals conceded, they will also have allowed one of their highest goal totals over a single season. The defence has so far yielded 31 in 29 matches, so a final reckoning in the region of 40 wouldn’t be too surprising. United’s previous defensive low point saw them concede 45 goals in the 1999/00 season, coincidentally the same year they were at their most prolific at the opposite end of the field. Anyone with a ticket for a United game at the turn of that decade were guaranteed goals.

No Premiership team has performed at a consistently high level as Manchester United over the life of the EPL. For example, Arsenal and Chelsea were locked together in the 1993/94 season, but in respectively 10th and 11th positions, rather than scaling their more common recent heights and Manchester City has not even been a permanent member of the elite division. Therefore, if we look at United’s Premiership record, we are comparing sides of genuinely consistent high quality.

Their two seasons where they concede more than usual, but also score at a more prolific rate, hints at an ability to score more goals, if required and if you plot total goals scored against total goals conceded for United over their Premiership life, the correlation is reasonable (r^2  0.21) and in the direction expected.

As well as conceding more often this term, United have also conceded the game’s first goal at an elevated rate for future Champions.  They have failed to land the opening blow in around a dozen league games and they were similarly generous in 1999/00. However, then as now they have stormed back to more often win matches where they have trailed at rates well in excess of those you would expect from even a top class EPL side.

This begs the question, is United, especially their attack, in horse racing parlance, an unexposed “horse” ?

Teams rarely win competitions by goal difference (you have to go back almost ten months to find the last occasion where the EPL title was decided in such a way). During matches, sides try to maximize their likelihood of winning the games, but they aren’t obligated to maximize the margin by which they achieve victory. 

International matches played in the early part of the century saw the top tier nations typically record 2-0 wins against the emerging European nations, as they adapted a safety first approach to winning such matches, especially when faced with well organised defences, but mediocre attacks.

United’s profile of greatly increased scoring ability when required to overcome a clumsy or unlucky defence is shared by Arsenal at their contending best, but no other teams exhibit it as a strongly repeatable trait.

An extremely high quality racehorse can often beat lesser rivals with very little effort and in doing so record performance ratings well below their true capabilities. The excess ability is obvious, but there is no need to demonstrate it. The sight of United trailing to virtually half the Premiership in 2012/13, yet still win "going away" in the majority of cases may be a manifestation of this extra ability being required to win a particular football match.

Are Manchester United, football's equivalent of a racehorse winning with something in hand?
If this is the case, it has implications for every ratings based attempt to predict match outcomes or even down to individual player ratings. The ratings you record and use are already subject to the different game states and match contexts in which they are measured, but increasingly for the best teams you may not know just how good a side can be until they experience a season where the concession of the opening goal swings toward expectable extremes.

As ever, bookmakers prices are the quickest place to validate these ideas. Average scoring rates, corrected and collected over time, to allow for opponent strength and home field advantage and then converted via a device such as a poisson to produce match odds, give good agreement with quoted odds for a wide range of run of the mill Premiership games. But this method often underestimates the chances of top sides, compared to quoted bookmaker odds. 

The professional modelers, it would seem are allowing for hidden and rarely needed improvement in the Premiership’s unexposed dark horses, such as Manchester United and Arsenal. When looking at the very best, there is unlikely to be a simple, linear correlation between their previously measured performance and their future predicted achievements.

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