Huge home field advantages in Aussie Rules football

The April, 2005 issue of "Journal of Sports Sciences" is dedicated to the topic of home field advantage (thanks to Drew for pointing this out in a previous comment), and I've started going through some of the papers. Here's one to start off.

It's by Stephen R. Clarke, and titled "Home advantage in the Australian Football League." And it found some interesting home field effects.

Most of the 16 teams in the AFL are located in the state of Victoria. It turns out that teams from outside Victoria have higher long-term (1980-98) HFA's than the others – quite a bit higher. The six "non-Victorian" teams have HFAs of 36, 25, 19, 17, 17, and 10 points, respectively. That's the top-five HFAs, plus one in the middle. (The overall average is 10.)

AFL game scores average around 100 points per team, so HFAs of 17 to 36 are pretty significant. From Table II of the study, it looks it takes about 100 points to turn a loss into a win. So Adelaide's 36-point HFA extrapolates to a home advantage of .360 – the equivalent of a .860 home winning percentage for an average team. (Of course, that advantage will be less if scoring overall is higher in Adelaide.) Clarke tells us that in 2002, the two teams from the state of Western Australia – who had HFAs of 19 and 17 points -- were 16-4 at home, but 2-18 on the road. (That doesn't include games against each other.)

Another way of looking at it is that, according to Clarke, the average margin of victory in the AFL is about 30 points. An advantage of 36 points where the average margin is 30, is, of course, quite significant.

Why does this happen? Clarke cites crowd effects. There are four teams that share a single stadium in Melbourne, and those teams have among the lowest HFAs. Clarke argues that the teams that play in the shared stadium attract not just fans of their own team, but fans of the opposition, as well as neutral fans. Also, the stadium (which holds 100,000) is usually not filled. Clubs that moved to the shared stadium have seen their advantage drop. And the one non-Victorian team that doesn’t have an outsized HFA is from Sydney, where AFL is "not the traditional game and crowds have not been strong."

Also, there's the "familarity" explanation. Opposition teams have at least four times as much familiarity with the shared stadium as any others, which may make their road disadvantage smaller.

Clarke does mention travel – some of the non-Victorian teams are some 2,000 km from Victoria -- but dismisses it on the grounds that (a) after a few years, the clubs should have got used to it, and (b) travel generally becomes easier over time, but the HFA is fairly constant.

Finally, there's weather. Some of the non-Victorian teams play in much hotter climates than Victoria, "and it is probably true that away sides have ... difficulty coping with this."

I'm not sure what to make of all this. For the shared stadium, it could be that the HFA is normal when an out-of-town team visits – but that when two "home" teams play each other there, the HFA disappears. And so the low observed HFA is just the average of a normal HFA and a zero HFA.

For the non-Victorian teams, the weather seems to be the most plausible explanation – running around for two hours in the very hot seems quite different from running around for two hours in normal weather. But, obviously, I don't really know.