Friday 17 October 2014

Your Biggest Opponent Might Be Your Teammate.

In attempting to answer the question “how good is a striker?”, the focus unsurprisingly falls on their goal scoring abilities. Raw goal scoring totals have been replaced by such statistics as “goals per 90 minutes” to reflect playing opportunity, often with corrections to remove penalty kicks and to allow for the different scoring environments that are present later in a game.

Latterly, actual goals have been replaced by expected goals, based on the likelihood that an average player would score with a shot or header from a particular location on the pitch. 

The ability to get into good scoring positions may be as important as the successful execution of a chance.

Random variation may in the short term produce actual goal tallies that flatter or under value a player and so his “virtual” goal per minute numbers may be a better indicator of his likely long term scoring potential.

The difference in talent levels at the very top level of finishing is likely to be very small and the ability to outwit the defence and fashion a chance may be more important than short term goal scoring achievements.

The opposing defence is quite naturally considered the natural opponent of a striker trying to amass expected goal value, but often there is also another factor that might cause his numbers to rise or fall.

Liverpool was fortunate to be able to call on two exceptional strikers, last season. Both Suarez and Sturridge reached impressive, respective goal totals, both real and expected. In addition, both missed playing time for a variety of reasons. But Liverpool was able to call on at least one of the pair for every Premiership game.

Suarez’s suspension left the striking stage clear for Sturridge at the start of the season and then the roles were then reversed when the latter missed a run of matches from early November to mid-January.

While in tandem, the two strikers could possibly be competing for the best chances created by their teammates, while in the other’s absence, each may have laid claim to the majority of the prime opportunities.

Therefore, I looked at each goal attempt made by Suarez and Sturridge over the 2013/14 Premiership season as defined by shot location and type. And, reflecting the wider picture, these primary parameters were significant indicators of whether a goal was likely or not to be scored.

I then added a variable to differentiate between when both Suarez and Sturridge were on the pitch and when just one of the strikers was present. This new variable was also a significant indicator of likely success, reducing the likelihood of a goal being scored when the duo were playing together.

In the case of Sturridge, his expected goal per game number falls from 0.9 when he flies solo to 0.67 when he partnered Suarez. A fall of nearly 30%.

The same is seen for Suarez, 1.1 expected goals per game alone and 0.75 when paired with Sturridge. Once again, this is a fall of around 30%.

We are looking at nearly 300 total attempts, but the results may just be a quirk of this dataset. However, on a shot by shot basis, it does appear that the players are taking a bigger proportion of low expectation attempts and fighting over the prime cuts when both are playing.

Suarez’s average goal expectation per attempt fell from 0.23 to 0.14 when Sturridge joined him on the field. Sturridge’s comparative figures went from 0.27 to 0.18 per attempt.

This is a single case involving two extremely high class finishers and there are at least eight other outfielders to consider, but it perhaps seems that the pair as a duo may have been shooting sometimes, when the position was too heavily defended.

This may have had implications for Liverpool’s strategy when both played, although it is now a moot point.

Perhaps more pertinently, each player appears to depress the expected goal record of the other by their considerable presence on the field. And this may have implications for player assessment as well as projection at future clubs, where the most difficult opponent to overcome in posting impressive scoring statistics may well be your teammate. 

Luis Suarez debuts for Barcelona in the near future. 


  1. I've done a stack of research on Karim Benzema & tossed around the idea that Ronaldo depresses the input of his teammates by taking up so much of the attack.

    Madrid take around 18-20 shots a game & if Ronaldo's on the pitch he's taking 7 of them; leaner pickings for the others. If he's not in the team, they still create a similar amount of chances and being Madrid are similarly successful but the shots get shared around more. Benzema's contributions when Ronaldo is off the pitch and in Ronaldo's position are really decent & make him look more elite than he does as part of the CR7 machine.

    Obviously Suarez at Barca is fascinating; he may not affect Messi's contribution significantly due to probably playing on opposite sides but Neymar is likely to suffer & whilst they will trounce teams, there only so many chances they will create. There has to be an ideal strategy and Barca look like they might end up with too many chiefs and not enough indians; which is something Madrid are going to find out too having sold great creators in Ozil and Di Maria & replaced with shooters like Bale, Rodriguez. It's like an arms race!

    I also think thatmaybe the Balotelli signing was an attempt by Rodgers to replace pure shot quantity with the hope that it would pay off with goals; as yet it hasn't.

    Anyway, nice article! :)

  2. I'd expected to see a lower chances or goals per game when both are on the field. Partly that's because they can't both make the run into the "best" position to receive the ball or they would crowd each other out. So one of them makes the unselfish run, thus creating less scoring chances for themselves.

    However I'm surprised at the lower conversion rates. I wonder how they compare to the players who were replaced?