What can we learn from attacking statistics?

Date published: Friday 30th December 2016 12:27

In this piece we’ll take a look at the most important attacking stats for individuals. If you missed it, go back and read Peter G’s introductory piece about context in statistics

 

Goals, Shots and Conversion Rate
Goals are an easy stat to appreciate. Your guy, or the other team’s guy, puts it in the net, and you add one to the total. Some goals are lucky, some are brilliant, but over the course of a season, most players’ total goals will be a good indication of their scoring contribution. Their positions on the pitch, and the team they play for, are crucial in determining how high that number is, but that’s just common sense.

Yet goals are in one way the most deceptive stat of all. They’re very rare events, and they absolutely determine the result, and so they naturally stand out in our minds. But to score a goal, a player has to do something else first: get in a good position to shoot. And it turns out that under certain circumstances, your shots can be a better indication of performance than your goals.

Here’s why. Conversion rate is the stat which tells you what percentage of your shots go in the net, not counting shots that are blocked. The average conversion rate for all players over the course of the season is usually around 11-12%. Here are the successive season-by-season rates for some of the Premier League’s longer-serving strikers, penalties excluded, ending with this season (Giroud not listed for this season):

Sergio Aguero: 19.2, 15.4, 23.6, 18.2, 21.5, 15.2

Olivier Giroud: 12.5, 17.0, 24.1, 18.8

Jermain Defoe: 15.5, 9.5, 22.0, 13.9, 15.3, 23.7, 18.5

Romelu Lukaku: 19.0, 20.8, 10.5, 19.8, 26.5

Christian Benteke: 21.9, 15.1, 18.8, 17.8, 13.6

The thing to notice is that conversion rates can be highly variable from season to season. If we count only the full seasons, Christian Benteke has the narrowest spread at 6.8%, with Aguero 8.2%, Lukaku 10.3%, Giroud 11.6%, Defoe 14.2%. A top striker can take well over 100 shots a season; last year the leaders were Kane 159, Aguero 119, Lukaku 118, Vardy 115. So even a 6.8-point swing can mean eight or more goals in a season, which can make a big difference in the table.

So here’s the point: if even the best strikers can have wide swings in conversion rates, the key to getting more goals is consistently getting more shots in good positions. In fact, it has been conclusively shown that players can get good shots much more consistently than they can finish them. The good strikers are the ones who consistently get good shots, and keep the more variable conversion rates well above average.

Shot quality is best measured by football’s most cutting-edge stat, Expected Goals (xG or ExpG). We’ll wait until the end of the series to talk about this stat, which in a way will sum up a lot of the material. But just remember that earlier this season, when the goals weren’t going in, Zlatan Ibrahimovic said, in so many words: “I’m getting good chances, eventually the goals will come.” He knew what he was talking about.

A brief mention of shots on target and shooting accuracy (percentage of shots on target). These are useful stats which tell you a bit about getting good shots and finishing skill, although expected goals and conversion rate tend to put them in the shade. I’ll leave it to you to explore them, so you can laugh or cry the next time a commentator says “he had to hit the target there”.

 

Assists, Key Passes and Chances Created
After goals, the attacking stat we hear most is assists. It’s easily countable and easily understood. Here are the top assisters over the past few years:

2014-15: Fabregas, Cazorla, Di Maria, Brunt, Sigurdsson, Hazard, Henderson, Baines

2015-16: Özil, Eriksen, Payet, Tadic, Silva, Milner, Mahrez, Alli, Lamela, De Bruyne

2016-17: De Bruyne, Lallana, Sanchez, Matic, Zaha

Notice that in 2014-15, Chris Brunt and Leighton Baines make the list. They’re not what you’d consider to be top passers. But they took a lot of set-pieces. Brunt led the league with eight assists from set-pieces that year, Baines had three. Fabregas topped the overall list that year with 18 assists, but only 11 were from open play. Second-placed Cazorla had only 11 assists, but 10 were from open play, because Mesut Özil was taking most of the set-pieces for Arsenal. So you need to check set-piece numbers to fully assess a season assist total.

Otherwise, most of the names on these lists are what we would expect, with a small surprise here and there. But assists are a stat that needs to be used with caution, for two reasons: 1) You get an assist if you’re the one who gets the ball to the scorer, even if the scorer does most of the work himself; 2) You only get an assist if you’re the last one in the build-up. To see some of the consequences, go on YouTube and check out Southampton’s three goals against Bournemouth from their game of 18 December.

On the first, Jordy Clasie makes a routine pass to the wing to Ryan Bertrand, who then beats two players and drives a superb shot from a difficult angle. Clasie gets an assist, even though Bertrand created the opportunity.

On the second, Sofiane Boufal sends Steven Davis through with a brilliant backheel, and Davis crosses for Jay Rodriguez to sweep home. Davis rightly gets an assist, but Boufal gets nothing, even though his contribution was equally necessary and more impressive.

On the third, Nathan Redmond dribbles neatly near the edge of the area, but Steve Cook slides in and both men get a touch, and the ball ricochets to Jay Rodriguez, who waits for a bounce, then smashes a brilliant strike into the top corner. Redmond gets an assist, even though the actual touch that sent it to Rodriguez may have been accidental.

These examples show why assists, if not useless, can be very misleading. They’re best considered in broad perspective, looking at the leaders after a full season, with careful consideration of set-pieces.

The same is true of their cousin – key passes. According to WhoScored, a ‘key pass’ is the final pass leading to a shot at goal from a teammate. The same rules apply for key passes as for assists, with the same problems.

So here too we have to be careful. If you hear that a player created four chances in a game, it sounds fantastic, but to evaluate the stat you have to look at the pass maps. Another player might have created only two, but those two might have led to much better chances.

At the same time, looking at these stats over a season, as with assists, produces sensible results. Here are the key pass leaders for the last few years:

2014-15: Hazard, Fabregas, Silva, Downing, Eriksen, Sanchez, Navas, Cazorla

2015-16: Özil, Payet, Eriksen, De Bruyne, Willian, Lamela, Tadic, Mahrez

2016-17: Payet, De Bruyne, Eriksen, Sanchez, Özil, Barkley, Firmino, Silva

There will be fewer surprises on the key pass lists than on the assist list, because the sample is significantly larger. Goals are rare and shots much more plentiful, so the leaders will naturally sort themselves out. The only semi-surprise on these lists is Stewart Downing, but remember he had an excellent year for West Ham in 2014-15.

So those are the major attacking stats. Things like dribbles and shots per game still need context, but are relatively self-explanatory. We’ll cover passing stats in a separate article. But next time we’ll go to a particularly thorny topic – defensive stats for individuals.

 

Peter Goldstein

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