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Shoot. The. Ball! Or Efficiency and The Shot Limit

By Ted Knutson | June 1, 2013 | Analytics

Earlier this week, I looked at Luis Suarez’s offensive efficiency in comparison to other star forwards around Europe. At some point in the future, we’ll probably combine all of the numbers I examined to come up with a single efficiency metric (sort of like OPS in baseball), but for now you can only say Suarez creates a lot of shots and key passes, loses the ball a lot, and is comparatively bad at turning his shots into goals.

The larger question here is this:

Why does efficiency matter?

In this particular case, we’re talking about offensive efficiency and it’s worth taking a second to step back and think about the endgame.

How do you win a football match?

Score more goals than the opponent. It's still a simple game, right?

Well, there are two parts to that statement. 1) Score goals. 2) Stop the opponent from scoring goals. Ignore the defensive side of the equation for now, and you come up with the objective for the offense: Score goals.

Now, how do you score goals?

Shoot. The. Ball.

Still obvious, right? But what if I told you there’s a limit to how often a team can expect to shoot the ball?

The Shot Limit
Over the last four seasons across the five major European leagues (392 team seasons), only two teams have averaged more than 20 shots per game. Chelsea averaged 21.9 per game in 2009-10, which was 3.6 shots more per game than the next closest team…  and they won the league by one point.

ronaldo shootsIn that same season, Real Madrid averaged 21.5 shots per game. They took 5.9 more shots per game than the next closest team in the league. Yet they only finished with four more goals than that team in the final table.

Most importantly, Real Madrid lost the league by three points.

Efficiency matters. And it matters more as teams start to brush up against the theoretical maximums.

In modern football, it is nearly impossible to shoot more than an average of 20 times per game across an entire season (at least in the big European leagues).  The best teams will exceed this number at home fairly regularly, but they’ll trail way off on the road, especially against good competition.

As a manager, if your system is producing an average somewhere near 20, you have to be pretty pleased, because it means your team is one of the best in Europe at creating chances. But just shooting isn’t everything – quality of chances matters too. Once you get to the point where you are averaging 20 shots per game, it’s basically impossible to find a way to shoot more often per game. The only way you can improve your return on goals is to become more efficient at converting shots.

A Liverpudlian Proof
This is where Liverpool comes in. As I mentioned in the Suarez article, Liverpool averaged 19.4 shots per game this season, which is close to the shot maximum. They could do a little better at limiting opponent’s shots, but systemically the offense was really good.  If you are rubbing up against the max shots limit, the only way you can score more goals is by being more efficient. And even at his best, Suarez is one of the most inefficient players around.

What’s really interesting in this particular case is that Liverpool averaged about the same amount of shots with or without Suarez this season (data courtesy of James Grayson). That’s not the type of production you expect when your superstar forward is out of the lineup.

Put together the facts, and you end up with this:

1)      Liverpool are brushing up against the shot limit.

2)      They create about the same amount of shots with or without Luis Suarez.

3)      Even at his best, Luis Suarez is one of the most inefficient players around.

Conclusion: If they want to get better at scoring goals, Luis Suarez is a luxury Liverpool can’t afford.

This isn’t to say Luis Suarez and his bag of tricks aren’t valuable. They are. They just aren’t that valuable to Liverpool. This is a team whose system is already creating a ton of shots, and in order to improve they need to maximize those chances, something Suarez detracts from. On a different team that doesn’t create that many chances, Suarez would likely still have huge value.

Efficiency and Player Recruitment
The reason I started examining efficiency at all is because I was looking at Key Performance Indicators for attacking players as a way to find and evaluate potential transfer targets. The first thing I came across that I felt was really important was Key Passes (and by proxy, assists).  The second thing is this general concept of player efficiency.

The immediate, obvious manifestation of this concept is in shot conversion rates for attacking players. In essence, how good is player X at producing shots on goal and/or scoring goals? Once you know that there is a shot maximum any particular system can achieve, the importance of player shooting efficiency becomes readily apparent.

I’ve just scratched the surface on the work I want to do in this area, but I have a very strong suspicion that we will see the importance of this concept crop up again and again as analysts examine both the very best and very worst teams, systems, and players.

Article by Ted Knutson