Like It Or Not, A Close AFL Game Really Is A Coin Flip

On the eve of the 2021 final series, Kane Cornes – one of football’s numerous ex-player-turned-pundits – observed that Port Adelaide, the club he played 300 games for, had gone undefeated that season in matches decided by small margins.

Cornes spruiked this stat as proof that the Power were a “mature, well-coached side.” Ironically for an ex-firefighter who carries a torch for making inflammatory statements, he probably didn’t expect that to be as controversial a claim as it was.

Fox Sports’ Max Laughton brought attention to an otherwise unnoticed tweet with a comment of just four words: “It says they’re fortunate.” Cue two dozen replies, most falling somewhere between mild indignation and outright contempt.

Of course, Power fans would remember all too well that an ability to win the close games, real or imagined, did not prove a relevant factor in their finals campaign. 

The brief euphoria of a 43-point win over Geelong in the first week of finals is now a distant memory after their season ended with a 71-point belting from the Western Bulldogs in a prelim two weeks later.

Flash forward to this weekend, and the first match of a new season. 

Port Adelaide’s opponent was the Brisbane Lions, who have themselves also been press-ganged into a narrative about the results of close games in recent years, one less optimistic.

Since their breakthrough return to the post-season under Chris Fagan in 2019, the Lions have played six finals in three years and tasted victory in only one of them. Twice they’ve exited finals in ‘straight sets’, both times losing a semi-final by less than a goal.

Their 1-point loss to the Bulldogs in the 2021 finals prompted plenty of discussion about just what was going wrong for them in close games. When their pre-season match against the very same side went down to the wire, all the talk was about how diligently they’d practiced that very scenario at training over the summer.

It’s only fitting then that Saturday night’s showdown between these two premiership hopefuls was the first match of 2022 to be decided by a margin of 12 points or fewer. The result, an 11-point win for the Lions, fits their narrative nicely – Port Adelaide’s, not so much. How can this be?

The answer is, and as Max stated it: Fortune. 

Sometimes it smiles upon you, sometimes it does not, but one thing you can count on for sure is that it will try tricking you into seeing patterns and narratives that aren’t really there.

Understandably, many find this perspective unpalatable, even insulting. The notion that close games are decided by luck mixes about as well with the feverish passion of rusted-on footy fans as oil mixes with water.

The word luck can make it sound as if all notions of cause and effect fly out the window as soon as a margin drops below two goals. Let’s put it this way instead: the results of close games are indistinguishable from the results of a coin flip.

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This chart shows the probability of various coin flip streaks. Flip two coins and the chance of getting two heads is 25%. Flip three, the chance of getting three heads is 12.5%, and so on.

We can compare AFL results to coin flips quite easily. For the purposes of this exercise, I’m looking at every team’s results from 2000 to the present day, equating wins to heads and tails to losses. Draws, not having a natural equivalent in a coin flip, are taken out of consideration entirely.

Before we look at coin flips and close games, let’s go in the other direction. This will provide a picture of what things look like when results are not random. Here’s how our coin flip steak probabilities compare to AFL teams’ winning and losing streaks in games decided by ten goals or more.

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The difference is stark. Each of the possible streaks we’re looking at is far more likely to be observed when tracking whether teams win or lose in AFL games with margins of 60+ than it is in a series of random 50/50 coin flips.

This provides proof to something no one would dispute: flogging an opponent by 10 goals requires more than just some good fortune. The reasons for this are straightforward – teams good enough to deal out losses of this magnitude aren’t typically bad enough to concede them, and vice versa.

The same is not true for smaller margins. Bad teams win by a handful of points just as often as the good ones do, and losing by that amount is no different. Now that we’ve seen how things look at the opposite end of the spectrum, here comes the comparison we’ve been waiting for.

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The streaks seen in coin flips and close games of footy could hardly be more symmetrical – particularly when contrasted with the previous comparison. Take away the labels and this chart would require to careful study to be certain there was any difference at all.

Still, seeing the numbers stack up may not make this reality easy to wrap one’s head around. The key is knowing that talk of luck and fortune does not discount the impact players have on a game. Rather, it is an acknowledgement that other forces have an influence also.

This is something we all know intuitively. To pay Port fans back for the earlier pain by ending on a high note, one of my favourite examples is the second of the two Showdowns in season 2013.

Trailing by 8 with only minutes left on the clock, Port Adelaide’s Angus Monfries launched a shot at goal on the run that seemed destined to be both too short and off-target. Enter: a miracle.

The ball struck the turf just meters from the behind line, and in the kind of bouncing brilliance that would make Stephen Milne sob, somehow twisted itself onto a totally different trajectory and went through for a goal.

Minutes later Chad Wingard kicked the goal that put the Power ahead and proved to be the winner, but it could not have done so were it not a stroke of luck so unlikely it seemed guided by divine hands (or perhaps Satan, if you happen to be a Crows fan).

Fortune good and bad takes many forms in footy – the bounce of the ball, the weather, the umpiring, the injuries, and whether the players woke up on the right side of the bed that morning. It’s what makes the game unpredictable and entertaining. 

And, when a match goes down to the wire, it’s what decides the result.

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