AFL Model Methodology

Match Prediction Model

Team ratings

Each team has an attacking and defensive rating which gets updated following every match.

Expected Margin

$\text{Expected Margin} = (\text{Att}_h + \text{Def}_h) - (\text{Att}_a + \text{Def}_a) + \text{Venue}$ Where

$\text{Att}_h$ denotes the attacking rating of the designated home team,

$\text{Def}_h$ denotes the defensive rating of the designated home team,

$\text{Att}_a$ denotes the attacking rating of the designated away team,

$\text{Def}_a$ denotes the defensive rating of the designated away team, and

$\text{Venue}$ denotes the net venue effect.

Updating team ratings following a match

These ratings are updated following each match based on the adjusted margin compared to the expected margin.

Expected scores

$\text{Expected}_h = \mu + (\text{Att}_h-\text{Def}_a)$

$\text{Expected}_a = \mu + (\text{Att}_a-\text{Def}_h)$ Where

$\mu$ is the AFL average score.

Adjusted scores

Adjusted scores are a weighted average of a team’s actual score and their score had they kicked at an expected accuracy. The expected accuracy is a weighted average of the competition-wide accuracy and the team’s accuracy in the current season.

$\text{Adjusted} = w\cdot(6\cdot\text{G} + \text{B}) + (1-w)\cdot(c\cdot(\text{G}+\text{B}) + (1-c)\cdot(\text{G}+\text{B}))$

Attacking rating

Each team’s attacking rating is updated based on their adjusted score compared to their expected score.

$\text{New attacking rating} = \text{Att}_h + k_t(\text{Adjusted}_h-\text{Expected}_h)$

Defensive rating

Each team’s defensive rating is updated based their opponent’s adjusted score compared to their opponent’s expected score.

$\text{New defensive rating} = \text{Def}_h - k_t(\text{Adjusted}_a-\text{Expected}_a)$

Venue advantage

Venue advantage is based on the following four factors:

travel distances for the two teams;
number of matches the teams have played at the particular venue over the past five seasons;
a constant home advantage which applies to all matches, with the exception of Grand Finals, where the designated home team is playing in its home state; and
historical performance of the teams at the particular venue compared to expected performance.

$\text{Venue}=\text{Travel}+\text{Venue Experience}+\text{Home Advantage}+\text{Venue Performance}$

$\text{Travel}=k \cdot ({\text{Travel}_h}^w - {\text{Travel}_a}^w)$ Where

$\text{Travel}_h$ and

$\text{Travel}_a$ are the travel distances in kilometres for the home and away teams, respectively.

$\text{Venue Experience}=k \cdot (({\text{Matches}_h + c})^w - ({\text{Matches}_a} + c)^w)$ Where

$\text{Matches}_h$ and

$\text{Matches}_a$ are the numbers of matches played at the venue in the past five years by the home and away teams, respectively.

Incorporating player information

The official AFL Player Ratings are used to supplement the Team Ratings in order to obtain an improved prediction based on the named team lineups for the two teams. Detailed information on the AFL Player Ratings can be found below.

For the purpose of this model, a player’s estimated rating for a match is calculated using a weighted average of their rating in previous matches with their latest match carrying the greatest weight. The estimated rating for all players listed in the team lineups are aggregated for each team.

$\text{Expected Margin}_p=w_s \cdot ((\text{Att}_h + \text{Def}_h) - (\text{Att}_a + \text{Def}_a)) + w_p \cdot (\text{Player Rating}_h - \text{Player Rating}_a) + \text{Venue}$ Where

$\text{Player Rating}_h$ and

$\text{Player Rating}_a$ are the totals of the estimated player ratings for the home and away teams, respectively.

AFL Player Ratings

Brownlow Medal Prediction Model

The Brownlow Medal prediction model uses an ordinal logistic regression model and was based on Chew The Stat’s Monte ChaRlo model methodology. The Wheelo Ratings model uses in-game statistics only which would generally not perform as well as a model which takes into account coaches and media votes.

Statistics

Match result and margin
AFL Player Rating points
Kicks
Handballs
Total possessions and contested possessions
Metres gained
Centre clearances and stoppage clearances
Total marks, contested marks and intercept marks
Hitouts and hit outs to advantage
Tackles
Frees for and against
Goals
Goal assists
Score involvements
Bounces
Spoils
Defensive one-one-one contests won or neutralised