http://www.soccerbythenumbers.com/2011/05/why-goal-value-of-corners-is-almost.html
A while back, I
wrote about the goal value of corners. Turns out that more corners don't equal more goals. Across the big leagues, the correlation between corners and goals is essentially 0 (it's strongest in the EPL at .06, and weakest in Serie A and La Liga at less than .01). The graphical representation of this pattern tells the story, keeping in mind that the average number of goals a team scores per match is around 1.3 across leagues and seasons.
So, statistically speaking, the offensive "value" of corners seems to be slim to none. Similarly, match outcomes appear to be
unaffected by corners. Assuming that earning corners is an indicator of offensive pressure, shouldn't teams that generate lots of corners also be teams that generate more goals? What gives?
One of the issues with the kind of analysis above, of course, is these data are based on match totals. As such, they are not designed to tell us the odds that any one corner actually yields a goal - they are simply match totals "macro-level data", so to speak - that are aggregated over the course of an entire match.
To dig a little more into the goal value of corners, what we ideally would also want is more information about the micro-level of play; that is, what exactly happened after any one corner was taken and whether it yielded a goal. More specifically, we want to know what the odds are that any one corner kick ends up with a team putting the ball in the back of the net.
So to get a better handle on this issue, the good folks at
StatDNA generously dug into their treasure trove of in-match data and helped me to calculate shots and goals scored from corners for a reasonably-sized sample of about 12-14 Premier League matches from this season. Shots and goals created from this particular match situation are defined here as occurring
within three touches of a corner.
We can think of goals produced from corners as a simple chain of events: corners lead to shots, and shots lead to goals (of course, some corners
are direct shots and thus some goals are directly scored from corners). So I wanted the know the following:
- What proportion of corners actually produces shots on goal?
- What proportion of shots created from corners produces goals?
- And overall, what is the ratio of corners to goals?
Of course, we would expect some slippage along the way. Not every corner will produce a shot on goal, and not every shot on goal will go in. As a consequence, the ratio of corners to goals is likely to be smaller than 1. "But how how much smaller?", inquiring minds will want to know. And where does most of the slippage occur?
In case anybody cares.
