This has been a hell of a week for arguments about the structure of the AFL, so we’re going to devote most of this week’s “preview” to casting our eye over some of them.

The fixture is fine, shut up about the 17-5 plan

We’re on record, having looked at strength of schedule in the AFL fixture, as arguing that within the confines of 17 opponents and a 22 week season, the current method of fixturing works pretty well. As the number of double-ups in the current draw is limited, and the double-ups seem to be balanced throughout the ladder, the end result is a relatively fair draw. It’s not perfect, but pretty close and leaning in the direction of handicapping top teams which is good for competitiveness. We’ve found that the difference between easiest and hardest is no more than 1 expected win throughout the season.

However, it seems that “relatively fair” isn’t good enough. It must be perfect, scream the fans and concerned football writers across the country (or at least on Twitter and the comments of the Herald Sun).

Specifically, two proposals have been put forth: the “17-5 draw” and a 17 round season. We can dismiss the idea of a 17-round season out of hand. It would involve each team playing each other once, alternating home and away year-on-year. It would mean less football, an increased chance of a bad team sneaking through to the finals, and increase the role of luck in the final outcome of a season. It would be more unfair to players, and to fans who like watching football.

It is a terrible idea.

The 17-5 fixture proposal seems to be gaining ground, which worries us.

Seventeen-Five

The seventeen-five draw is a modified version of a system used in the Scottish Premiership (their version of the EPL). It sees every team play each other once, then split into two, six team pools play one game against every other team in their pool. The teams are locked into their pools, which often has 7th on more points than 5th and 6th. It also sees dramatically reduced interest in many of the late season games, as they have little to no impact on the final results.

For the AFL, the proposal sees teams locked into three tiers of six teams. Confusion reigns over whether teams can move up and down from these tiers after being assigned in, or if the points accrued will be wiped after the first 17 rounds or not. We suggest that the most sensible version of the model is:

Teams can’t move higher on the ladder than the highest spot in their tier; and

Points are retained from the regular season.

If this happened, immediately 25 games would become almost worthless (the bottom tier) except for devoted fans and slop addicts. It’s highly likely that many of the mid and upper tier matches would turn into dead rubbers as well, as has been the case in the Scottish Premiership.

We’ve gone back at worked out what the tiers would have looked like for 2014 and 2015, taking the first time each club met rather than just the first 17 rounds:

In 2015, Geelong would have been guaranteed a spot in the top six, where in reality they missed the finals, while Richmond would start out capped at 17th based only on percentage. Fremantle would be all but guaranteed a spot in the top 4, with GWS and Collingwood finding it extremely hard to make the eight but also unable to drop further down the ladder. Very few substantial changes would be made to the actual ladder however, just more meaningless matches introduced.

In 2014 even less movement is displayed in the top tier, which might allow for more shuffling of places. However, three teams are almost immediately ruled out of the race for the final two spots in the eight, significantly reducing the tension and anticipation in the mid-tier (including Richmond who eventually made the top 8). This is because the loser of the first game between Adelaide, West Coast and Richmond would essentially be eliminated, and the loser of the next one would be eliminated as well.

Whilst it may raise the stakes for a limited number of games, it would dramatically lower them for far more.

The problem with this approach is the very existence of hard absolute lines cut through the ladder at 6th and 12th. As soon as you have such boundaries, you start getting anomalous and unfair results on both sides of that boundary. It seems a recipe for cheapening the first 17 rounds of the season, preventing exciting runs late in the season, and creating more dead rubbers.

If a change must be made, perhaps the fairest suggestion has been made by the of Footymaths Institute. It suggests a floating conference system be implemented either before the season, rendering the current method of draw weighting more explicit and balanced. His full proposal is the preferred on by HPN. Other than the current system, of course, which seems to be working just fine.

Tanking is fine too

Some of the footy world seems to confuse tanking with match-fixing. Thus we had this week, with the reemergence of the “tanking debate”, a number of proposals (such as a draft lottery) to remove the “spectre” of something that cannot actually be removed. We’ll have more to say about this in future but for now here’s the abridged version:

The AFL world has been a bit confused by the past ugliness, thanks to priority picks, of teams throwing specific games to stay under 4 wins to get a priority pick – but that is something closer to match fixing and something the AFL rightly looks to prevent.

The essence of tanking is decisions made which hamper immediate competitiveness but pay off in the long run. Such behaviour can occur through week to week selections, experimental player roles, injury management and trading strategies.

All of these things have valid benefits for weak clubs in the longer term, and they also make the acquisition of high draft picks more likely. There is a natural and deliberate synergy between sacrifice for long term gain and high draft picks. Clubs can and should do these things, and we need to be more realistic about the desirability or possibility of stopping such things.

The impact of rain on scoring (or: bonus points are a bad idea)

This week Josh Jenkins, now writing for ESPN, revived a suggestion that AFL teams should get a bonus premiership point if they score 100 points in a game. This isn’t a great idea for a number of reasons.

Perhaps the strongest objection, beyond this being a solution in search of a problem, is that it would stop percentage from being the tiebreaker on the ladder on many occasions. This should actually undermine the stated aim of the bonus point (promoting offensive football) by discouraging dominant teams from racking up scores where bonus points already separate them from needing percentage to get clear of near rivals. It could even create situations where teams become extremely defensive in order to prevent a ladder rival from reaching 100, rather than trying to increase their own percentage by scoring a lot.

However, another significant objection is that a sport played in winter in different cities and at one venue with a roof is not a level playing field when it comes to scoring. How much impact does weather have on games?

To produce this data we’ve taken 15 seasons of matches, and linked each venue with daily rainfall from the nearest Bureau of Meteorology observation point with daily rainfall totals, treating Docklands Stadium as never having rainfall. Bear in mind that daily rainfall doesn’t allow us to distinguish games where the match occurred before rain fell that day, nor games impacted by rainfall from the previous day.

As we can see, the presence of any rain on matchday reduces scoring by nearly 5 points, impacts on accuracy, and impacts on total scoring shots. Medium and heavy rain fairly naturally has a greater impact, with medium rain (above 1.8 mm daily rainfall) reducing average scores by a full goal, and heavy rain even moreso. Scores over 100 occur 10% less frequently in heavy rain than in no rain.

So how does rain differ between cities?

In essence, Adelaide and Gold Coast are drier than Sydney and Brisbane, which are both drier than Melbourne, which is drier than Geelong and the Tasmanian cities. This is the order in which a bonus point system would provide relative advantage.

Note however that Launceston, Perth and Sydney feature disproportionately among the wettest 5% of matches. This is also especially true of the Gold Coast where from a relatively small sample, heavy rain days are more common than light ones. Geelong’s rainfall, though frequent, tends to be lighter (the difference between Geelong and Melbourne surprised us).

Let’s translate the data into teams:

The teams who play mostly at Docklands or in Adelaide are clearly experiencing less rainy matches than MCG teams and those in the wetter capitals. Given that GWS and Gold Coast have only existed since the 2000s drought broke, they’ve faced more wet weather – games impacted by rain have become more frequent in East Coast cities in the 2010s.

We can also translate each team’s home games into an expected rain impact based on past results:

Hawthorn, playing home games in Launceston and at the MCG, are the most likely to experience wet weather, followed by Geelong and the Perth teams. The Perth teams and the Swans can expect the most games impacted by heavy rain, followed by GWS whose Canberra games are more likely to be dry.

At the other end of the scale, the Bulldogs and Saints should only experience home wet weather in their rare forays to Cairns or Yarra Park, and should be the most relatively advantaged by recieving a bonus point for high scores. The next group of teams that would gain an advantage are the other predominantly Docklands sides, plus Gold Coast and the Adelaide teams.

Clubs already will find their percentages impacted somewhat by their balance of wet vs dry games. They can at least ameliorate the imbalance of percentage-boosting opportunity by defending well in rainy conditions. We see no reason to build a new systemic imbalance into a system already imbalanced by fixture strength and the climactic and venue impacts on percentage.

What to look for this weekend

1. Carlton should beat Brisbane in the midfield

Carlton’s win over Geelong was one of those fantastic extremely improbable wins that make sport worth watching, but there’s a risk of recency bias leading us to overrate the Blues. Our own strength ratings, which look at overall records for the year and compensate for opponent strength, tell us that forward and defensive strengths are evenly matched against each other:

Brisbane has some specific weaknesses that Carlton might be able to exploit. One is the likely positive hitout differential gained by Kreuzer and Phillips over Martin and West (5th in the league vs 5th worst). Brisbane’s clearance ratio is also good for worst in the league, winning just 0.77 clearances for each clearance won by their opposition. Carlton are a more respectable 10th, at 0.99. These factors are likely somewhat responsible for Carlton’s greater midfield strength rating and suggest they should win here, though maybe not by as much as the 1.28 betting line suggests.

2. There’s no expectation that Melbourne should beat Hawthorn so they probably will

Melbourne has made a habit this year of losing games they enter as favourites, while putting up very good performances in games where they’re not fancied. We’re not suggesting they’ll roll the Hawks, but inconsistency is an inherently hard thing to predict. This game presents as one where they might defy the odds. Let’s find some reasons why!

In terms of efficiency inside 50-metre arcs, the two teams are pretty similar – both slightly below average in defensive strength with Melbourne having somewhat better offensive strength.

According to the HPN ratings, Hawthorn has a much stronger midfield than the Dees (120% vs 99%), but the HPN ratings consider just one factor: inside 50 differential, a statistic which correlates very well with winning. However, when looking at other factors that also somewhat correlate with a team’s success, Melbourne’s inside unit seems to have the upper hand. Melbourne, as led by “Big Maxxy” Max “GAWNDOG” Gawn, have dominated in hitout differentials (1.30 to 1) this year, whilst Hawthorn has faltered so far (0.98 to 1). In addition, Hawthorn has shown a propensity to lock up the ball where possible for stoppages – they are currently #1 in the league for total stoppages in their games, something which should play right into Melbourne’s hands. Additionally, Melbourne have been far more effective in gaining clearances than Hawthorn this year.

If Melbourne can convert their apparent inside midfield strength into better balance on the outside (and thus inside-50 entries), this may be a path to victory. Even if not, expect the story to be one of Melbourne’s inside dominance being nullified by Hawthorn’s dominance in space.