Home > Theory > Shot Stopping vs Preventing Shots Revisited

Shot Stopping vs Preventing Shots Revisited

In a previous post I suggested that for a goalkeeper shot stopping is more valuable than preventing shots. By using some simple maths I showed that at real world save% levels (c. 60-80%) increasing save% by 1% is 1.5x to 4x more valuable than decreasing SoT/match by 1%. In this post I will build on that by looking at how often goalkeepers come to catch or punch crosses and how valuable those aerial contributions are using data from the first 16 rounds of the 2010/11 Bundesliga season. [1]

Goalkeepers face a lot of crosses every match. To be more specific, based on the data a goalkeeper faced on average 20.5 crosses per 90 minutes, or roughly one cross every four and a half minutes. Despite the high volume of crosses coming their way the average goalkeeper is passive in dealing with them, making only 1.24 catches and 0.83 punches per 90 minutes on average. Of all the crosses they face goalkeepers catch or punch only 10.1%. [2]

Of course some goalkeepers are more active in the air than others. The most active goalkeepers dealt with c. 15% of total crosses – Weidenfeller (15.2%) and Neuer (14.9%) – while the least active dealt with c. 6% – Sippel (6.4%) and Mondragon (6.2%). If we look specifically at the most dangerous crosses, the crosses into the six yard area, the average goalkeeper deals with only 32.8% of them and even Manuel Neuer, arguably the strongest goalkeeper in the world when it comes to aerial ability, deals with only 52.5%.

The relevant point is that even the most active goalkeepers deal with only a small minority of crosses. In addition to the low volume of aerial contributions there is also the question of how valuable each contribution actually is.

Let’s look at it from another angle and ask how valuable is a cross on average? If we simplify the question a little we could say that the value of a cross depends on three things:

1. What percentage of the time the cross finds a teammate
2. What percentage of the time the teammate is able to convert the cross into a shot on target
3. What percentage of the time the shot on target results in a goal

Intuitively it seems clear the value of the average cross is very low. The three-way parlay of finding a teammate, getting a shot on target and the shot resulting in a goal is very unlikely. According to a stat from @Orbinho via @11tegen11 in the Premier League the average cross leads to a goal only 1.6% of the time, so the value of a cross is 0.016 goals.

If the value of a cross is so low then the value of a goalkeeper dealing with that cross must also be low. If the average goalkeeper claims two crosses per 90 minutes and the most active goalkeepers claim just under three (Neuer 2.75), then the value of being elite at claiming crosses is c. 0.015 goals per match. Contrast this to shot stopping were the value of being an elite shot stopper is c. 0.2-0.3 goals per match.

In summary, crosses are a high volume low value action. Even the most active goalkeepers deal with only a small minority of total crosses, and each contribution has only a small value. The value of preventing shots by dealing with crosses pales in comparison to the value of shot stopping.

Something I didn’t address is the psychological benefit of having a goalkeeper who is good in the air on your team. I can’t speak from the perspective of a high level player but as a fan I know having a goalkeeper who is poor in the air fills me with fear and worry, and having a goalkeeper with a strong aerial presence has some positive value beyond simply the value they create by dealing with crosses. However I find it very difficult to believe that value could ever be enough that I would rather have an elite aerial contributor than an elite shot stopper.

I would also add that my view on the psychological benefit is that it comes not so much from dealing with a lot of crosses but more from simply not making any mistakes when you do deal with them. There are few things more frightening in football then seeing your goalkeeper flap at a cross, and that can have a negative effect on a team’s confidence. I don’t think a goalkeeper who mostly stays on his line but when he does deal with crosses does so confidently would have anywhere near the same kind of negative effect.

[1] I would have used the first 17 rounds to get the full first half of the season but the data for the 17th round was unavailable. The sample is also missing the match between Mainz and Stuttgart from the first round due to incomplete data.

[2] Goalkeepers do also drop some crosses (roughly 1 in every 20 matches on average according to the data) and sometimes come for a cross and miss entirely which is not reflected in the data (some keepers more than others of course) which would increase the actual value by a few tenths of a percent.

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Categories: Theory
  1. David Turner
    June 18, 2011 at 08:20

    Erm, but the crosses that a goalkeeper is most like to parry are the more dangerous ones, right around the six yard box, no? Not all crosses are equal, and goalkeepers opting out of playing those crosses seems like it would increase the value of the crosses.

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