Classifying Grand Finals (A Reprise)

(This piece originally appeared in the Guardian, and revisits the topic of defining a typology for Grand Finals, which I first looked at in 2009 where I came up with a similar solution, and again in 2014 where I used a fuzzy clustering approach.)

For fans, even casual ones, AFL Grand Finals are special, and each etches its own unique, defining legacy on the collective football memory. 

At another, coarser level though, we can see similarities between different Grand Finals – consider, for example, the 2010 Pies v Saints draw, as well as the 2005 and 2006 Swans v Eagles nail-biters. And then, for contrast, recall the 2007 Geelong v Port Adelaide rout along with last season’s comfortable Hawks victory by 46 points and their similarly comfortable 63 point victory of the year before that.

In some sense then, there are different types of Grand Final – but how many types are there and how should we define them?

There is, of course, no definitive answer to that question, but a statistical technique called cluster analysis allows us to come up with one view. To perform a cluster analysis of Grand Finals you need some way of mathematically calculating the similarity between any two of them in a way that captures meaningful differences.

One metric that does this is the lead, and how it alters across the course of a game. Our classification then will group Grand Finals on the basis of how similar or different was the pattern of lead changes and the magnitude of those leads.

Specifically, we’ll use the following pieces of information:
•    Did the eventual winner lead at Quarter Time? At Half Time? At Three-Quarter Time?
•    By how much did they lead at Quarter Time, Half Time, Three-Quarter Time and Full Time?

Based on those seven pieces of information, the 117 Grand Finals (excluding the drawn ones because they don’t have an “eventual winner”) can be classified into six fairly distinct types, some characteristics of which I’ve summarised in the following table.

Note that, where this table uses pie charts to denote proportions, the darker the circle the closer is that proportion to 100% and the lighter the circle the closer is that proportion to 0%.

So, for example, the very first circle tells us that 100% of teams in Grand Finals classified as Coast-to-Coast But Mostly Close led at Quarter Time. Also note that the pie charts used for each era, which appear at the far right of the table, sum to 100% if you add down across all Grand Final types for a single era.

With that in mind, here's a little about each Grand Final type:

The Coast-to-Coast But Mostly Close Victory

(Yeah, the names do go swiftly downhill after this one.)

The key characteristic of this Grand Final type is that the winning team tends to lead at every change, but not by much. This makes them, at least in terms of the closeness of the scores, relatively appealing Grand Finals to watch.

There have been 34 Grand Finals of this type in V/AFL history, the most recent in 2013 when Hawthorn led Fremantle at every change by between about 2 and 4 goals and went on to win by just 15 points. 

Grand Finals of this type are often won by only narrow margins, 20 of the 34 having been decided by less than 3 goals, and 27 of them by less than 5 goals. The average victory margin is about 3 goals.

Across history, Grand Finals of this type have occurred about 30% of the time, though their frequency has fallen off markedly since the early 1970s as average scores have tended to increase, after which there have been only six (1974, 1976, 1977, 2005, 2006 and 2013).

The Come-From-Behind Victory

In this Grand Final type the winning team tends to trail at every change, and always at Three-Quarter Time.

There have been only 9 instances of this type, the most recent in 2009 when St Kilda led Geelong at every change before going down to them by just 12 points at the final siren.

All but two of the Grand Finals of this type were won by less than 3 goals and the type includes a number of particularly memorable Grand Finals. The famous 1970 Grand Final in which Carlton kicked 5.4 to Collingwood's 1.1 in the final term to complete a stunning victory is an archetypical example.

Another, from slightly more recent times, is the 1984 Grand Final in which Essendon trailed Hawthorn by 21, 25 and 23 points at each of the three changes before scoring 9.6 to 2.1 in the final term to win by 4 goals.

Come-from-behind victories have been rare in every era of the V/AFL and the 2009 classic is the only one in the past 30 years. They have the lowest average victory margin of all the types at just over 9 points.

The Second-Quarter Scare Victory

This Grand Final type is characterised by the fact that the eventual winner leads at the first and the final change, but almost always trails at Half Time.

There have been 15 Grand Finals of this type, five of them occurring since 1980 (1982, 1997, 2001, 2004 and 2011). 

The most recent example was the 2011 Grand Final in which the Cats led the Pies by a single point at Quarter Time but lost the Second Quarter to trail by 5 points at the main break. They then led by 7 points at Three-Quarter Time before going on to prevail by just over 6 goals. 
Final margins in these Grand Finals have tended to be small, with about half of them (7 of 15) decided by less than 3 goals and about three-quarters of them (11 of 15) decided by less than 5 goals. The average victory margin has been just over 3 goals.

The Nervous Start Victory

In all Grand Finals of this type the winning team has trailed at Quarter Time but at neither of the changes thereafter.

There have been 19 GFs of this type, including seven since the mid-1980s (1987, 1991, 1994, 1996, 2002, 2008, and 2012).

In that 2008 game the Hawks trailed the Cats by 1 point at the first change then steadied to lead by 3 points and then 17 points at the second and third changes respectively. They won, eventually, by 26 points.

The 2012 edition saw the Swans trail the Hawks at Quarter Time by 19 points then kick 6.0 to 0.1 in the Second Quarter to lead at Half Time by 16 points. They then clung on to lead by a single point at Three-Quarter Time before going on to register a 10 point victory.

This type of Grand Final includes a number of large victories, over one half of them (10 of 19) decided by 5 goals or more, those last two examples notwithstanding. The average victory margin in this type of Grand Final is 32 points.

The Coast-to-Coast Blowout Victory

These are the Grand Finals that disappoint the emotionally uninvested fan most of all. The key characteristic is that the winning team leads at every change and tends to win going away.

History has produced 34 of these GF types, 16 of them since 1980, coinciding with the trend towards higher scoring (1980, 1983, 1985, 1986, 1988, 1989, 1990, 1993, 1995, 1999, 2000, 2003, 2007, 2010, 2014 and 2015).

Last year’s Grand Final, which saw the Hawks lead the Eagles by 19 points, 31 points, and then 50 points at each of the changes, before going on to win by 46 points, is a quintessential example of the genre.

Almost 80% of Grand Finals of this type (27 of 34) have been won by 6 goals or more, and about 55% (19 of 34) by 8 goals or more. The average victory margin is almost 52 points.

The Game of Two Halves Victory

In Grand Finals of this type, the winning team trails at Quarter Time and Half Time but wrests the lead by Three-Quarter Time and doesn't surrender it.

There have been only 6 Grand Finals of this type in history, and none since 1998 in which year Adelaide trailed North Melbourne by 8 points at Quarter Time, and 24 points at Half Time, before rallying in the Third Quarter to lead by 2 points at the end of it and then running away with the game in the final term to win by just under 6 goals.

In these games the winning teams tend to heavily dominate the second halves, to such an extent that the average victory margin in Grand Finals of this type is just over 6 goals, and only two of them have been won by less than 5 goals.

Grand Final Leads

The two most common types of Grand Finals are the Coast-to-Coast But Mostly Close and Coast-to-Coast Blowouts, defining characteristics of which are that the winning team leads at the end of most if not every quarter.

In fact, if you look at the all the quarter-end changes across all 117 Grand Finals, the team that ultimately won has led at the end of:

  • 70% of First Quarters
  • 76% of Second Quarters
  • 90% of Third Quarters

Looking just at the Grand Finals since 1990, the percentages for First (65%) and Second Quarters (73%) are lower, but a startling 96% of eventual winners have led at the final change.

The only team from that period to come back from a deficit at the end of the Third Quarter was Geelong in the 2009 Come-From-Behind Grand Final covered earlier.

By way of comparison, across the 206 games of 2016 so far, the ultimate winner has led at the end of the First Quarter 71% of the time, at the end of the Second Quarter 86% of the time, and at the end of the Third Quarter also 86% of the time.

So, as in regular home and away season games, teams leading at the changes in Grand Finals have very often gone on to win, but, particularly in recent Grand Finals, leading at the final change has proven especially predictive of the ultimate outcome.

Year-by-Year Details

Not every Grand Final fits one of the six descriptions from earlier perfectly, but each Grand Final is, in a mathematical sense, closer to one of these six types than to any of the others. It’s on that basis that the 117 Grand Finals have been categorised.

In the four charts that follow, for each of these 117 Grand Finals I’ve shown the lead (or deficit) for the eventual winner as at the end of a particular quarter.

The years are colour coded by Grand Final type and their labels have been offset, where necessary, to avoid overlap. Where that’s occurred a line has been drawn to the point where the label should actually be (ie at the correct margin).

These charts show the range of leads and deficits for each of the Grand Final types at the end of each quarter, and also reveal the categorisation of every Grand Final. 

What might we expect for the 2016 Grand Final?

We can employ other techniques to fit a statistical model to previous Grand Final results to estimate how likely it is that we’ll see any of the six different types this year.

A reasonable hypothesis is that the likelihood of each type depends on the relative abilities of the teams taking part. It’s less likely, for example, that we’ll see a Coast-to-Coast Blowout if the two teams are especially well-matched.

To create a model then, I’ve chosen as inputs the estimated offensive and defensive strengths of the teams facing off in the Grand Final. As well, bearing in mind the variability in the relative frequency of each Grand Final type across the eras as shown in the earlier table, I’ve also included the era in which the Grand Final was played.

The final model (which, for the technically curious, is a Generalised Boosted Model) seems to fit history fairly well and estimates the probabilities for the 2016 Grand Final as follows (the frequencies for era from 1995 to 2015 are shown in brackets):

  • Coast-to-Coast But Mostly Close: 25% (14%)
  • Come-From-Behind: 8% (5%)
  • Second-Quarter Scare: 11% (19%)
  • Nervous Start: 22% (19%)
  • Coast-to-Coast Blowout: 27% (38%)
  • Game of Two Halves: 6% (5%)

So, the model suggests that a Coast-to-Coast But Mostly Close game is more likely and a Coast-to-Coast Blowout less likely than a naïve scan of recent history would otherwise suggest.

That seems sensible when we consider the relatively similar demonstrated abilities of the Swans and the Dogs, especially in recent weeks, and the fact that both are better known for their defensive than for their attacking qualities, which makes high-scoring (and hence blowouts) less likely.

That said, the model still (narrowly) rates a Coast-to-Coast Blowout as the most probable scenario.

Let’s hope it’s wrong …

(UPDATE: Subsequent to finalising this piece for the Guardian, I came up with another chart that shows the score progressions at the end of each quarter for all the Grand Finals of each type. It appears below.)