Know your Stats: The Key Pass

In my last piece, I started looking at the importance of properly contextualizing player performance in order to isolate what we --  as fans, managers, and coaches --truly care about: ability and value. In this piece, I'd like to show how it is that advanced metrics can help out in that difficult task.

I'm very partial to passes. Passing is my favorite part of the game. Nothing trumps a side that can pass the ball around fluidly, and aesthetically nothing beats a beautifully threaded through-ball to a put a forward in scoring position. Therefore, a metric that I'm very partial to is the "Key Pass". First, let's begin by defining the Key Pass. Per Opta Sports, the company that measures and tracks the metric, the definition of the Key Pass is:

The final pass or pass-cum-shot leading to the recipient of the ball having an attempt at goal without scoring.

So there we go. The definition provides a standard for the people at Opta to objectify events, and it makes the data they provide very reliable, moving away from subjectivity. Opta essentially has large number of people sitting in their viewing center (or working remotely, maybe?) counting Key Passes. Sounds like a fun job. Unless your assignment is to track Crystal Palace games or something. 

The Key Pass metric provides one big advantage over assists,  and that advantage can be found in the final clause of the definition: "without scoring". The Key Pass is a better way to unveil the true measure of what a player is actually doing on the field.  Let's view this through an example of an one of the best playmaykers in the world, Mesut Ozil, who has averaged around 4 Key Passes per 90 minutes over the past few seasons -- an impressive figure.

Say Mesut Ozil filters a beautiful ball from midfield in  between the two center backs. Last season, Cristiano Ronaldo would have been on the receiving end of such a pass, and Cristiano Ronaldo, being the monster that he is, probably would have buried the ball in the back of the net (the guy breaks hands from 30 meters – a goalkeeper a few meters away has no chance). Now, this season, Nicklas Bendtner could be on the receiving end of those passes, and it is just as likely that Bendtner will trip over his own feet as it is that he scores.

Observe Nicklas Bendtner in his natural habitat

So we have two situations where Mesut Ozil makes the exact same pass and gives his forward the same chance of scoring – let’s say an *85% chance. The 15% left to actually score the goal will be decided by 1) the scorer’s ability and 2) random chance (say a beach ball getting in the way). Neither 1 or 2 actually tell us anything about Mesut Ozil. And it is 1 and 2 that determines whether Ozil's pass gets tallied up as a an assist.

*Note: these percentages are mere abstractions to make my point.

Now, expand that situation to a much grander scale, where a creative midfielder plays with only Bedntners and no Ronaldos. I’m inclined to say his assist numbers would not be as high with Bendtners as they would be with Ronaldos. 

Now, this is not to say that the Key Pass Metric is a flawless measure. This article from Statsbomb does a fairly good job at evaluating the Key Pass, pointing to one big flaw: not all key passes are created the same. In the example given above, say instead of Ozil filtrating a perfect ball that leaves the forward on a 1 v 1 with the goalkeeper and with an 85% chance of finishing, he puts a little too much on the ball and instead leaves the forward at an awkward angle with the goalkeeper and only with a 70% chance of scoring. Also, not every final pass is equally as "key" -- there is a big difference between a  ball played from midfield to put a forward through and a short tap in pass in the keeper's box.

Over many different observations (instances), these differences are meaningful, and they are directly a result of a player's ability. However, the Key Pass is a great starting point and a vast improvement over the statistics we have typically had to contend with. Anyway, I strongly recommend the Statsbomb article; it actually attempts to normalize for the differences in the quality of the Key Pass using another metric called Expected Goals (ExpG). It shows the type of improvement that we can continue to make in soccer analytics.

My initial intent with this piece was to actually start engaging in analytics and to track Ozil's career based on the Key Pass. However, the availability of soccer statistics is very limited, and the availability of advanced soccer statistics is even more limited. I have put in a request to Opta to see if they will grant me access to their data, which they do grant to bloggers and writers as long as their projects merit it. Hopefully I get access to it, and the quality of my content on this space can go up a notch.

I'll leave you with some passing gems from Ozil:

And in case you were wondering about the significance of the picture at the beginning of the post, here are some gems from one of the masters of the Key Pass, Carlos Valderrama:

Around the Web:

• Richard Whittall with a short but thought provoking look at football finance and the possibilities of teams...GASP...actually spending their money wisely and not indiscriminately.
• Statsbomb with a similar piece, suggesting improvements over the decision making organization that most teams employ in an effort to improve that word we all love: efficiency.
• Over the weekend: Barcelona, Real Madrid, and Atletico Madrid combined for a 16-0 trouncing over their opponents. Gotta love the parity in La Liga. I'm just gonna keep hitting the snooze button, sadly.
• A World Cup Draw simulator! The most competitive field ever?