When Is A Chance Not Really A Chance (Or Even A Shot)?
This Thursday sees the inaugural Opta Pro Analytics Forum, an event which will see lots of top football analysts meet up to share their work, and I have been fortunate enough to be invited to attend.
As chance would have it, whilst compiling data for my Chance Quality project earlier today, I noticed a curious anomaly that I had not come across before, and a request for clarification on Twitter lead to an eye-opening debate.
I had always thought that the definition of a created chance was one of the more straight-forward in the world of football analysis. As Opta explain on their definitions page, a key pass (one which creates a chance) is:
"The final pass or pass-cum-shot leading to the recipient of the ball having an attempt at goal"
Seems simple enough; Player A gets the ball to Player B, with the latter then taking a shot. Or so I thought... Take a look at this from the recent 0-0 draw between Chelsea and West Ham, which is taken from Stats Zone. What do you notice?
West Ham managed to create two chances whilst only having one shot. In view of Opta's definition above, how is this possible? Surely an attempt at goal (a.k.a. a shot) was required?
This is how it's possible. We can see Downing racing clear to the byline. He then puts a cross to the far side of the box.
As the next picture shows, the ball reaches Andy Carroll successfully:
However, as a Liverpool fan, I'm sadly familiar with what happened next. Despite Downing putting the ball on plate for him, Carroll could only manage a mis-kick/air shot at the vital moment.
This was recorded as a created chance, so it therefore turns out that it is possible to create a goal scoring opportunity without the pass recipient having a shot after all. Who knew?
Thankfully, people on Twitter did. @TotalFootballFC, the creator of the excellent Stats Zone application, advised me of the following:
Aha, so this is what Carroll managed to do. I've probably never discovered this before because if a team had an average amount of chances and shots it would not come to light, as any such discrepancy on the chance and shot front would not stand out. @colinttrainor was on hand to ask the question that I would have had I been online at the time:
Apparently you don't need a shot, and the plot thickens, as @RyanKeaney, the editor of OptaJoe explained:
Hold the phone. Downing created a 'Big' or what is also called a 'Clear Cut' chance with that Carroll air shot? If you're a fan of analytics, this is big news.
In some ways, this is fair enough. Downing did what is asked of him, and got the ball to a team-mate in a fantastic position; it's not his fault that the aforementioned colleague is not, in this instance, a particularly prolific striker. In that sense, he should receive credit for the achievement.
But at the same time, I'm not sure amateur football analysts realise that this is the case in this situation. I know people assess how well a team has done in a match based in part on how many clear-cut chances they create and allow, so this discovery has potential implications there too.
I'm aware that this finding is of minimal interest to your average football fan, but it certainly interested me. If only I could find out how common this sort of chance/non chance is....
Roll on the OptaPro forum!
Recent related posts you might like:
PLCQ: Twenty Game Round Up - Which teams have been creative in the best areas, and/or restricted their opponents too? Includes a look at which teams have got more or fewer assists than my model suggests they should have.
Liverpool’s Chance Champion – A look at which Reds have created the most chances in 2013/14, and who has found the best areas most frequently.
LFC Pass Combination Heatmaps 2013/14 – A look at which players have been most involved pass-wise, and who they’ve linked up with in every league match this season.
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