Given that they’ve just lost the Premiership on goal difference this might seem like a strange time to be posting this. However I said recently that Manchester United had a poor total shot ratio (by their standards anyway) and if it continues at the same level it’s sure to catch up with them (link). I want to expand on that point here:
The plot below has three lines.
Red = 38 game moving average of Manchester United’s total shot ratio
Black = TSR of 0.500, the league average
Green = TSR of 0.632, the average TSR of a premiership champion
The first thing to point out is just how close they’ve been to the green line for most of this time – they’re the only team that has been this good for this long.
To summarise the pattern, United played at a consistent 0.600 level until the summer of 2003. A one season drop to the 0.550 level was followed by a one year dramatic rise to their peak, at 0.650. They then stayed at a remarkably high and consistent level until the summer of 2009, at which point their performance began to slide. Right now they sit at about 0.560. This drop off over the last two years is a pretty significant one. A team with a TSR of 0.632 will typically score 90 points, at a TSR of 0.550 we’re more talking an average of just 60.
One way to explain these variations could be United’s activity in the transfer market. The plot below is the same as that above but this time the ‘major’ personnel changes have been marked:
I’m not sure how much of a swing we can pin on the purchase or sale of one player. In the NHL it looks like losing a star player can cost the team about 2% of it’s TSR (link). Those players typically play ~40% of the time on teams that are half the size of a football team so I wouldn’t be surprised if the effect was at least as large in football as in hockey.
With that in mind, a combination of introducing Rooney and Ronaldo into the line up around the same time seems to coincide well with the rapid rise in ’03-04. I doubt that those two introductions explain all of the improvement but it would certainly contribute some amount. Conversely losing Ronaldo and Tevez together at the end of the ’09 season seems to coincide quite well with the start of the decline.
So what are your thoughts. Is this slide something you expect to continue, stop or reverse in the coming year? How dependent is it on United’s transfer policy over the summer? How few points would United have to score before you were genuinely surprised? 80? 70?