The value of disruptive runs. Or, why Firmino is such a valuable player for Liverpool

The key problem when scouting football players is knowing how they contribute to their team’s performance. A powerful answer to this question comes from looking at how much a player’s actions increases or decreases the chance of his or her team scoring. This approach works very well for on-the-ball actions. In particular for shots (it is exactly what expected goals measures) but also for passes and defensive actions, such as interceptions and blocked balls.

But…there are 22 players on the pitch at any time, all of them contributing to their team’s performance. It isn’t just the player who has the ball who determines how well a team plays. It is the movement of all players, in both attacking runs and defensive pressure, which determine the outcome.

A player who exemplifies the problem of limiting ourselves to on-the-ball event data is Roberto Firmino. He is often referred to as ‘underrated’ by commentators, because although he doesn’t score as many goals as Mohammad Salah, it his off-the ball movement which often creates space for his teammates. Radars for on-the-ball attacking stats for these two players are given below.

Firmino’s stats are certainly good. They put him top 10% among strikers for various passing metrics in the final third. But they miss a central part of his game…

To get an idea how we might measure Firmino’s skill we need to start with an example. One of his runs against Everton is shown below. Firmino is running out to the edge of the box, dragging a defender with him.

Wijnaldum makes the pass more central instead to Mane, but as the pitch control figure below shows, Firmino (marked as a star) opened up space for a possible pass to him. He ensured that the Everton defence was moving to the left wing (three blue players with arrows pointing towards the space Firmino is running in to), while the ball then goes towards to the area in front of the D of the box. Firmino’s run disrupted the defence.

Firmino (star) opens up space for a potential pass. Coloured arrows show direction of players (blue Everton, red Liverpool). Black arrow shows the pass that was made centrally to Mane.

There is nothing exceptional about this particular run. It is just a nice example of something Firmino does non-stop. He is always looking for and finding ways to open up space around the box. Sometimes he gets the ball, sometimes he doesn’t, but either way the movement is there and the defence is disrupted.

There is no way to measure this type of movement without combining event data and tracking data. What we have done is created freeze frame data of every action where event data is supplemented with tracking data from Skillcorner showing the position and direction of all players near to that action (i.e. in the frame of the TV broadcast footage).

Once the freeze frame data of a pass is created, we then evaluate movements in a variety of ways. We say that the value of the space opened is determined by the value of the best possible pass to that point. To determine this, we multiply pitch control (probability of receiving a pass and illustrated above) by pitch value (probability of scoring given a pass succeeds) and then we find the point which gives the maximum value. This essentially gives the probability a team will score if the pass is made, again returning to the fundamental way in which we measure all actions. This is shown below.

Probability of team scoring given a pass (is found by multiplying probability a pass will succeed with the probability a team will score given the pass).

The more central pass to Mane was roughly the same value as the space Firmino opened up.

The image below gives examples of Firmino’s sprints where he was the target of the pass and received the ball. When he does get the ball, it is is very often in the box.

We call the value of his Target Run Value. The bigger the diamonds below, the more value the run brought.

The value of a run is not just in the potential pass option created, it is also found in the pass that was later chosen. Below is a plot of where the ball went after Firmino did a run. We call this the Disruptive Run Value. These passes went to other players, but occurred at the same time Firmino carried out a space creating run.

We have two further measurements we use in assessing strikers. Potential Runs are the value of runs where he was the target of a pass but failed to receive the ball. This can been seen as both positive and negative: he opened space = good, but when the pass came he didn’t recieve = bad. Finally, we have Space Creation, which is the value of the space he created had the player on the ball chosen to pass to him (but didn’t).

Combining his attacking and defensive radars with his attacking radar gives a much fairer assessment of Firmino as a player.

An off and on the ball assessment of Firmino.

Now we see where he excels. He is the second best player per minute in the Premier League in terms of disruptive runs and space creation. Salah isn’t bad either (top 20% in these metrics), but he isn’t up to Firmino levels.

So far so good. Now we can put a number to why Firmino is so good. How can we compare to other strikers? And who is better than Firmino?

Here is a list of strikers in order of most value added by disruptive runs per 90.

At the top: Christian Pulisic. There is definitely a team effect here, in the sense that it is the top teams that are overrepresented exactly because they create more attacking situations. But it is very interesting to see Mitrovic and Bamford near the top of the list. In Bamford’s case, it is important to note that Leeds’ players nearly all score highly because of the system they play which demand a lot of running. But Mitovic would be an interesting player for any team who wants to better create space with runs, although it is also the case that he was very lowly ranked when it came to receiving the ball.

This article is the first in a series of about off-the-ball metrics using a combination of event data and Skillcorner tracking data. This work was done by Jernej Flisar, with Twelve Football. Our focus in the series is on evaluating playing positions that have proven difficult to assess with on-the-ball stats. In the next article, we will look next at why Kante is so valuable in midfield and then we will have a look at Burnley’s central defenders. Previously, we have used this type of approach in tactical work with clubs, but now we are confident in using it for scouting too. So if you would like access to our scouting tool and ranking, based on this approach, please send Twelve a message.

Professor of Applied Mathematics. Books: The Ten Equations (2020); Outnumbered (2018); Soccermatics (2016) and Collective Animal Behavior (2010).