When Manchester City dispatched Manchester United in commanding fashion earlier this season, the City steamroller was powerful, efficient, and impressive. It looked downright unstoppable. As Kevin McCarra noted the day of City's 6-1 trouncing of United in The Guardian, "For the football world at large, it is more significant still that City have 33 goals from nine league games. A club of such means does not usually inspire fondness from neutrals, but only a curmudgeon could fail to appreciate the accomplishment of City." Today, two months later and after beating fellow contenders Spurs 3-2 over the weekend, City still sit atop the Premier League, seemingly the team to beat this year.
So all is well at the Etihad, or so it seems. But are City still in a league of their own? The data below tell us that, despite the impressive goal difference revealed by a glance at the league table, City's offensive steamroller has slowed down. In fact, as a comparison across all 20 clubs shows, City is the club that has seen the most significant deterioration in offensive performance since the early days of the season.
Don't believe me? Take a look at the following graphs of some simple statistics. The first shows clubs' goal production for each week of play, up until Week 20 of the season. The dots show the number of goals; the lines show the trend.
Clearly, between Weeks 1 and 10, City were on an astonishing run. But, as the numbers reveal, this trend was not sustained. Statistical tests show that the trend in goals for City this year are best approximated by a quadratic function. This tell us that, after high level of scoring for the first half of the first half of the season, there has been a noticeable decline in City's offensive production.
Just in case you want to take a look at City's numbers in greater detail, here they are again for good measure.
Of course, any reasonable person might ask "How could there not have been a decline?" They were off the charts, and this may simply have been unsustainable. So if the team over-performed early in the year, what we are looking at is simply regression to the mean, and we should see a decline in performance across different dimension of offensive play as the season wore on. So let's take a quick look at two indicators: first, chance creation; second, efficiency.
As the next chart demonstrates, some of the drop-off in City's offensive performance has been due to a decline in chance creation. As the season progressed, City were less dominant than they had been earlier in the season - teams may have started to figure out ways to play them or City simply had a few bad days at the office. Both are plausible and would create the pattern we see.
But interestingly, we have also seen an uptick in shots since Week 14, while goal production continued to decline. So what explains this?
Efficiency, measured by the goals to shots ratio, played a role. Here, there's been a significant drop between Week 15 and 19, helping us to account for some of the overall trend.
Taken together, then, the data tell us that both shot creation and finishing explain some of City's coming back down to earth. First, there was a significant decline in shot creation between Weeks 1 and 13 from an incredibly high level of over 25 to a relatively low level of less than 10. And, unfortunately for City fans, when shot creation finally recovered, efficiency waned. Having an Adebayor around the training ground may have been helpful at that point.
It's easy to make too much of these numbers, in particular because we are looking at some very general indicators and a small sample of matches (20). But it's safe to say that Manchester City's offensive production has hit a couple of snags both in the chance creation department (early in the season) as well as the finishing department (later on). I suspect both of these are normal fluctuations, and that the club is still in a great position to win the league this year. But nothing in these numbers would lead me to assume that this will be anything other than a long, drawn-out battle between a City team that has come back down to earth and several competitors that are ready to pounce. The good news is that, if City are able to rediscover their offensive prowess from the early season and find a way to keep more clean sheets, they'll be able to control their own good fortune. And that's a great position to be in.