Part IV: "We've Got the Close One!"

So 2017 was great because Victorian fans had more to cheer about and because there were better match-ups each week. We've ruled out an increase in upsets. If your team is a massive underdog, and your team playing at home isn't Geelong, then odds are that they won't win. But what about the close-ones, when the underdogs gave the favourites a scare? Did 2017 have more of these type of games?

If we have a look at the distribution of winning margins since the VFL/AFL began (moving from dark red in 1897 to dark blue in 2017), we see that winning margins have tended to increase over time, with more recent seasons having higher margins. The abnormal seasons are 1922 which had 30 out of 72 games decided by 2 or 3 goals. And in 1907, 31 out of 68 matches were decided by 2 or 3 goals. Now that’s competitive!

Figure 18: Distribution of winning margins by season. 1897 is the dark red end of the spectrum through to yellow. green, then dark blue in 2017

If we summarise the data, the trends in mean and median margins echo the above. We see that the mean margin really picked up after 1976. It does beg the question of what caused this. We do know that the 70s were when teams (or some groups of players at least) were starting to be paid as professionals. 1975 was also when regular season matches were broadcast on television in colour. My guess is that this brought larger audiences, more advertisers dollars to broadcasters, more value for broadcasting rights, and finally more funds for clubs to invest in training facilities. And with some clubs adapting to this new professionalism better than others, a new gap in on-field fitness developed ensuring that some teams could maintain a run-on in a match for longer. Ground maintenance also may have improved in the late 70s so that higher scores could be kicked. 

For this discussion however, what's more important is that the mean and median margins came down in 2017, having reached an all time peak in 2012 (mean of 42, median of 42). 2017's mean margin of 31 was a level not seen since 1998. The median margin of 25.5 was a level not seen since 2007. There had been a fairly long period of dull matches between 2011 and 2016 inclusive.

Figure 19: Mean and median winning margins by season.

Let's dissect this trend a little more. If we look at the spread of margins over time below, there are even small jumps in the 20th percentile after 1980, which rose to 14 points. 1 in 5 matches have been decided by more than 2 goals for quite some time. But by far the largest increase is at the higher end with a huge leap in the number of blowouts from the mid-70s onwards, then coming back down in the mid-noughties (arguably due the more defensive style of play pioneered by Paul Roos' "winning ugly" Swans). But large margins started to re-appear from 2006 onwards. By 2016, 20% of matches (the 80th percentile) were decided by almost 11 goals. Boring. Thankfully, this came back a little to 52 points in 2017. Perhaps we noticed this in 2017, that more matches were more competitive than in the recent past. And while no-one wants "winning ugly" to come back into fashion, let’s hope this is the start of a downward trend in blowouts.

Figure 20: Winning margin percentiles by season.

One obvious hypothesis for this period of high winning margins (2011-2016) was the entrance of Gold Coast in 2011, followed by Greater Western Sydney (GWS) in 2012, that perhaps these teams were being belted week after week. Below shows the proportion of losses for the two largest losers in the competition each season. In 2012, it certainly was Gold Coast and GWS representing 31% of all losses but other teams featured from 2013 onwards. That recent spike in 2013 was when GWS (20%) and Melbourne (17%) represented 37% of total losses (and had 3 wins between them). In 2014, it was St. Kilda and Brisbane (18% and 14% respectively). In 2015, it was Carlton and Brisbane (both 13%). And in 2016, it was Brisbane and Essendon (18% and 15% respectively).

Figure 21: Share of losses among the two biggest losers each season. Filtered to 1925 onwards when the VFL became a 12 team competition.

So they did get belted initially but mostly what seemed to happened is that by soaking up draft talent from the 2010 draft onwards (and Essendon falling foul of the law), other teams were also being belted week after week. And it’s ironic that as part of pushing the game in Queensland by adding Gold Coast, the AFL have inadvertently kept Brisbane near the bottom.

Looking at it from the other angle, the period between 2011 and 2016 was also distinctive in that the top 4 teams were very dominant. The worst season was 2011 when the top 4 only accounted for 4% of the season's losing margins. Geelong, Hawthorn, Collingwood and West Coast only lost 14 games between them, a record low. For supporters of other teams, it does not get more boring than 2011. Luckily, things got back too normal in 2017. The top 4 lost 27 times in 2017, a level not seen since 2009. This reinforces the earlier finding that not only week-to-week match-ups were more even in 2017 but the top teams lost more frequently. The AFL's socialist paradise re-emerged in 2017 and this was another reason why we thought footy was so great. May they never add two teams built from scratch in non-AFL states again.

Figure 22: Share of losses among the four smallest losers each season. Filtered to 1925 onwards when the VFL became a 12 team competition.

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So with margins coming back to some level of normality and the top teams also copping their fair share of losses, I want to look at one last angle to assess the quality of the competition - the comeback. Even if it’s not an upset (which we saw earlier are not any more common than they've ever been), or even a close margin in the end, at least it might have been close at three-quarter time. Even better, when might have seen more team's bouncing back in the last quarter to retake the lead and seal a victory (personally these are my favourite games to watch, when the Dees are down but storm home). 

Let’s first look at how a team’s chances of winning have varied based on the situation they find themselves at each quarter-time break. Below is the trend of the home team’s rate of winning if they are behind at the breaks. We see that if the home team has been behind at each quarter, then their chance of winning is around 10%, and this has been the level for around 30 years. If the home team was up in the 1st qtr, then the chances of winning are slightly higher, and if the team is only down at the 3rd (after being up in the 1st and 2nd), then it is now almost a 50/50 shot at winning. Put another way, home ground advantage is worth a little more of late.

Figure 23: Incidence of the home team winning for different quarter-time scenarios by season.

If we look from the opposite angle, home teams being up at the breaks and then losing, we reach a similar conclusion. Away teams have little chance of winning (just under 10%) if they’ve been down at each break, Even if they are up at three-quarter time (but the home team have been up at the 1st and 2nd change), the away team’s chances are just as slim. There is a “wet-sail” factor evident as well. Even if the away team was up at the first two breaks but conceded the lead at the final break, they have little chance of recovery. The home team will go on to win around 80% of the time. This has been the case since the 90s and is not unexpected given the expansion of the competition outside of Victoria and home ground advantages intensifying. 

Figure 24: Incidence of the home team losing for different quarter-time scenarios by season.

So, it’s one thing to look at the likelihood of winning and losing but let’s see if these "foregone conclusion" scenarios are more prevalent than before. The good news is that matches where the home team leads, or scores are even, at every change is relatively flat, a touch under 40% of all matches (recall that the home team goes onto win over 90% of the time). The bad news is that matches where the home team is losing at each change has risen to a high level to represent around 30% of matches (and the home team has a 10% chance of winning these). And 2017 was no different.

Other variations are no more common than they've ever been. Where we saw earlier that home teams had an increasing advantage in this HT- > HT- > HT+ scenario, those matches are still relatively uncommon (5% of matches).

Figure 25: Incidence of match scenarios each season. 

Putting it together. If we take the HT- > HT- > HT- > HT win and the  HT+ > HT+ > HT+ > AT win scenarios as the definition of a comeback then we see below that 2017 was a good year, the best since 2005. In 2017, they were 9% of all matches. The best home team comeback of 2017 was Geelong playing North at Docklands and North were up at every change, 25 points going into the final quarter, and managed to lose by a point. There were 8 comebacks by away teams in 2017. The best was arguably Sydney coming back from a 29 point deficit at quarter-time against Richmond at the MCG in Round 13, clawing that back to a 13 point deficit at three-quarter time and going on to win by 9 points. Good times for Swans fans.

Figure 26: Comebacks by season. A comeback is defined as either of these scenarios:  HT- > HT- > HT- > HT win and the  HT+ > HT+ > HT+ > AT win.

Now, the definition of a comeback need not be purely defined by the margin at every change, but also the margin at three-quarter time, regardless of who was leading at previous changes. Below we can see a home team’s chances of winning based on this margin. Chances of winning sharply diminish if the home team is down by 3 or more goals or the away team are down by 2 or more goals.

Figure 27: Match result by home team's three-quarter time margin. All seasons since 1897.

And the chances of the home team coming back hit a recent high in 2017, home teams winning 11% of the time, even though they are down by 3 goals or more at three-quarter time. This is similar to what we saw earlier with home ground advantage becoming more important. Away team's chances remain slim.

Figure 28: Chance of a three-quarter time comeback for different scenarios by season. 

So let's add these to our tally of comebacks and we see below that comebacks represented over 10% of all matches in 2017, the best result since 1995. The best home team comeback was the aforementioned match where Geelong came back against North. Freo also managed to do it twice, once against North, coming back from 24 points down at Subiaco, and also coming back from 23 points down against the Bulldogs. There were 3 away team comebacks as well, the best being Brisbane at the Docklands vs Essendon in round 15. Essendon somehow managed to blow a 19 point lead at three-quarter time.

Figure 29: Comebacks by Season. A comeback is defined as either of these scenarios:  HT- > HT- > HT- > HT win,  HT+ > HT+ > HT+ > AT win, HT down by 3 goals or more at three-quarter-time and winning, or AT down by 2 goals or more at three-quarter time and winning.

So there you have it. In terms of the quality of the competition, footy did indeed suck between 2011 and 2016 (unless you followed the premiership team of course) but 2017 was a remarkable year on many fronts. Finally, the distortions created by adding Gold Coast and GWS to the competition seem to be behind us (including, for me, the "lost decade" for Melbourne Football Club). Brisbane Lions may yet start to show something too. Here's to a fine 2018. Footy!