AFL Statistics Series #6: Who Loses The Ball?

In this post on AFL statistics, I am going to focus on losing possession of the ball.

When in AFL matches turnovers are mentioned, I expect the image that comes to mind for many football fans is a player kicking the ball straight to the opposition, pretty much the type of action the term ‘clanger’ was invented for. As shown in the last post of this series though, the majority of disposals that lead to turnovers are not what are considered ‘clangers’; more often they are just ‘ineffective’ disposals, and about as often they are actually what are considered ‘effective’ kicks. At the same time, clangers are surely a considerable part of turning the ball over. Here I’ll take a closer look at how significant they are.

Clangers by themselves are fairly good at predicting how many turnovers a player will have (see chart below). One main difference between clangers and turnovers is that free kicks against a player are counted as clangers. Free kicks against though will to some extent not result in turnovers, either because the opposition is already in possession of the ball or because the free kick against has happened in a stoppage – particularly for rucks and inside midfielders. Hence in predicting turnovers we may want to differentiate between free kicks against and other ‘non-free kick’ clangers.

Turnovers and non-free kick clangers have a slightly tighter relationship (see chart below). If I am using a regression to estimate turnovers, one that separates out free kick and non-free kick clangers looks like it will give a more appropriate estimate of the relative importance of these things in predicting a player’s turnovers. But given many turnovers are not clangers let’s look a little further.

I might be able to do better using ‘disposal efficiency’. Ultimately though, one of my main intentions in this series to build up to a system of player value over the past twenty years or so, and there is not a long history of that statistic. So I am going to look at just raw disposal counts instead.

Average turnovers per game and simply average kicks also have a strong relationship across players (see chart below). A few players like Shannon Hurn, who are phenomenal in their kicking accuracy, will lie outside the trend, but in general kicks look like they will help to explain some of the variation in turnovers that clangers by themselves do not.

Handballs will too, but to a lesser extent – your team is more likely to keep possession through handballs than by kicking the ball. I haven’t shown it here, but there is a positive relationship between average handballs per game and average turnovers across players. Again there are some outliers from the general trend – rebounding defenders will tend to have more turnovers per handball, and rucks and midfielders will tend to have less, but there is something to be gained in predicting turnovers by throwing them in.

Putting all of these things together – non-free kick clangers, kicks, free kicks against, and handballs – we get a pretty good estimation of a player’s average turnovers per game (see chart below).

Ultimately, using kicks and handballs implicitly assumes that every player is as good as each other in retaining possession. It’s the clangers – in part also standing in here for disposal efficiency – that add the information about a player’s (in)ability to keep possession.

Though even just concentrating on the player in possession may give a somewhat incomplete picture of who is responsible for the turnover. Since many turnover happen in contests, perhaps some of the ‘blame’ should also go to the player that was on the intended receiving end of the disposal. Still, this should give something to work with in terms of attributing responsibility for the end of a team’s attack.