Possession per Shot on Target

I’ve always had an obsession with statistics. Do you pay attention to the statistics bar which runs across your screen during post-match interviews on Match of the Day? I do. Do you have a look at the ‘Match Facts’ after a game of FIFA? I do.
I love to look at the statistics to judge the success of teams in matches. But I’m not stupid, I know that stats don’t tell you everything. That forms part of my intrigue; you can get stats for virtually everything that happens in a game but they can still miss something. If you look through my previous articles you may notice me refer to stats a lot, but I also raise the point that there isn’t a statistic for ‘best player’ when writing if Lionel Messi could ever be called the greatest of all time. How about a statistic for the greatest team? I wonder if it can exist, but I have thought up a statistic that interested me enough to do some research into it; the possession-per-shot-on-target.
First, I’ll try and explain why I don’t think some other stats are indicators of which team is the best – so you can maybe understand where I’m coming from.
Win percentage: The team which wins the most is the best, yes? Well, who are they playing? We don’t know by looking at this stat. If a team has a win percentage of 73% we don’t know if they’re Barcelona or a Sunday League team, and you can’t call a Sunday League team the best in the world. The strength of the league also comes into question here.
Possession: If you’re looking at this stat and judging teams by it, you’re assuming that every team values possession of the ball. And they don’t. Not every team are Barcelona, some are like Stoke and look to play a direct ball as soon as they can. I’m not criticising, every team has their style and that’s what makes the game what it is. This makes me uneasy with judging by single statistics like this.
Territory: A relatively new statistic and one that I admittedly don’t use as much as the others. It’s an interesting stat that it always worth looking at but doesn’t tell the story of the game. If a team has most of their possession inside their own half, is it because the opposition are pushing them back or is it because they are holding onto a lead? We don’t know, and it’s important because one event would see them as the weaker team whereas the other would be the result of them being the dominant team.
Now, my statistic, the possession-per-shot-on-target. I’ll shorten it to P/SoT from now on. What I like about this stat is that it measures a team’s effective possession; it asks how usefully they use the ball. It’s calculated simply, you divide a team’s possession by the number of shots on target that they had in that game. Let’s say a team has 50% possession and has 5 shots on target, the P/SoT is 10. Using this as a yardstick let’s now say that the team instead has 2 shots on target (a poorer effort), this means the P/SoT is now 25. One more change, the team instead has 40% possession with 5 shots on target (same number of shots but with less possession); the P/SoT is 8. So the lower the P/SoT, the more efficient the team has been. The number is how much possession they have for each shot on target that they have.
So what does measuring the effective possession mean? Well a team can dominate possession and play most of the game in the opposition half and have 6 shots on target, ending the game with 60% possession. Now the opposition have had to play on the counter attack and have managed 4 shots on target, with 40% possession. Both teams have a P/SoT of 10; they have used the ball equally as well as each other. If we were using possession or territory to judge how good a team is, we would conclude that the first team is the best. Not so. Make sense? I hope so.
Now I had to apply this stat to many different teams, five in total. First I used both Manchester Clubs. At the time of researching, United were top of the table so should have had the lower P/SoT. In the first 20 games of the Premiership, United averaged 8.75 shots on target and 54.8% possession: a P/SoT of 6.26. Their best score came in the 1-1 draw with Swansea, they had 54% possession but a phenomenal 16 shots on target: P/SoT is 3.38. This was their best game in terms of effective possession but they could only draw the game. Interesting.
City now. They had an average of 9.2 shots on target per game and 54.8% possession (the same as United). Their P/SoT was 5.98. The difference is marginal between the two clubs, but the side 2^nd in the league had the more effective possession. A sign that they’re better or a flaw in the validity of the statistic? Draw your own conclusions. City’s best score came in the 3-0 home win against Sunderland; 16 shots on target with 61% possession this a P/SoT of 3.81.
Next I looked at both Liverpool and Stoke; two teams in a similar league position but also with contrasting styles. However Liverpool had a far superior P/SoT with 5.82 compared to Stokes 10.23. Is this unfair on Stoke? Or does it show that Liverpool aren’t nearly efficient enough with their conversion of chances? It’s hard to say, and this harms the statistic – we don’t know the context. Maybe if we could compare the P/SoT of all the other Premiership teams then we would know, but alas the author does not have the patience to do so! Considering that Liverpool’s score is lower than even the Manchester clubs, we must conclude that their conversion rate is shockingly low (but also that they are actually a very good team).
I wonder, are you now thinking about Barcelona? If this statistic tells us the best team in the world, then what is the score for the best team in the world?! Well, I’ll just give you the number. 9.36. Yes, Barcelona have possession stats that go off the scale (66.06% on average, but a record high of 77%) but Liverpool, City and United all have more shots on target than them. They managed only 3 shots on target against Zaragoza, they also scored 3 goals, and had 63% possession.
I feel that this introduces the single problem with my effective possession statistic, it assumes that teams are always trying to score. If a team is two or three goals up in a game, it is highly likely that they would retain possession to try and kill the game off, slow the tempo and reduce the atmosphere. They are keeping the ball but not taking any shots, so their P/SoT will rise and rise. This may be the case with Barcelona. Again, context is needed; the team must be trying to score in order for this stat to apply.
So there we have it, the possession-per-shot-on-target. I think the scores are interesting and I find it an intriguing concept. However I don’t think that it’s the ideal stat to measure how good a team is, my mind will keep on searching for another one. If you ever wonder just how well a team has performed, divide their possession by their shots on target: 6 is an average for a top team.
Just as a leaving thought, I came across an extraordinary game in my research. Stoke 2 – 0 Swansea. Yes, I said extraordinary. Swansea possession: 74%. Shots on target: 0. Stoke managed 5 shots on target with only 26% possession.
Stats are accurate up to 31^st December 2012
Stats for Liverpool, Manchester United, Manchester City and Stoke came from bbc.co.uk/football
Stats for Barcelona came from fcbarcelona.com
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