Tuesday, April 10, 2012

Did City Run Out Of Luck? Diagnosing Manchester City's Season

A lot has been said these last few days about the apparent "implosion" of Manchester City's title quest this season. And if The Guardian is to be believed, Roberto Mancini has six games to save his job. So what went wrong for Mancini and the Citizens?

Data can help settle arguments, so I thought I'd take another look at some basic performance indicators to see how the City's performance developed over the course of the season. You may recall that I wrote about City's midseason offensive struggles back in January (here and here). Then, the data told the story of a team that had had a truly phenomenal start to the season, but by January had come back down to earth. Their level of performance just didn't seem sustainable. So what has happened in the interim?
First things first: does offense or defense seem to be the more obvious place to look for the source of City's troubles? Here are the most basic of indicators: goals scored and conceded (the line indicates if there is a linear trend in the data).*

The trend lines couldn't be clearer: while City's defense has remained steady in allowing goals, there is a clear downward trend in offensive production. As I said back in January, during the first three months of the season, City's offense just shot their opponents' lights out (other offensive and defensive performance data not shown here bear this out, too.).

The question then becomes: what happened to City's offense? Did their production just decline steadily all the way through today? The answer may surprise you: City actually performed quite consistently most of the year - with one exception I'll get to in a moment.