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Player ratings: frequently asked questions

April 26, 2013 4:00 PM

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A revolutionary algorithm has been used to rank every player in the AFL

What is the Official AFL Player Ratings system?
Determining the best player in the AFL has always been tricky. Whether it be umpires, coaches, media or fans, judgements about top players have always had a large element of opinion.

Now, using the most sophisticated algorithm ever applied to our game, we can assess every single action of every player, determine the impact of that action and provide points – either positive or negative – toward that player's rating compared to his peers.

And unlike every other system, Official AFL Player Ratings are based on a player's past 40 games, a scheme that provides a long-term view of a player's standing within the AFL.

Who is the best player in the AFL? The revolutionary new player ranking system

We've also created positional ratings so that while a player may not appear in the top 10 or 20, fans will be quickly able to determine who is the number one defender, ruck, forward or midfielder.

Along with the obvious acts such as goals, marks and disposals, we've included intercepts, spoils, kicking to a contest, smothers, chasing, corralling and many other 'one-percenters' - along with where and when they occurred - to paint a complete picture of ever player's impact on a game.

While we're confident the system is the most sophisticated and detailed ever created for the AFL, we'll continue to monitor results, take fan feedback and consult the top experts to ensure Official AFL Player Ratings is the most accurate statistical view of our game.

How is each player's rating worked out?
Players accrue or lose points every time they are involved in a passage of play, and the score awarded to them each time they are in the play is determined by a complex algorithm formulated and refined over a number of years by Champion Data. Whether players accrue or lose points is based around whether they have a positive or negative impact on the passage of play.

A player's rating is determined by adding together his points tally based on a rolling window of the previous two seasons. For example, after round six of the 2013 season, a player's rating will be based on matches from round seven of the 2011 season onwards. However, only a player's most recent 40 matches are used in the calculation of his rating. This builds in a buffer for players missing matches through injury, suspension, omission or by not being involved in finals. A player's most recent 20 matches are given maximum weight in determining his rating and matches 21 through 40 are progressively reduced from 100 per cent weighting to five per cent for the earliest game in the window.

Which acts a player makes on the field contribute to his score?
Every time a player is involved in a passage of play he will have the chance to accrue points. But rather than his score being a simple tally of his possessions, marks, tackles, hit-outs, free-kicks and scores, his performance will be measured using a system called Equity Ratings. The system determines where and how a player influences a contest and whether the player's effort then results in a positive result for his team. Equity Ratings includes what coaches love to describe as "pressure acts". As a result, players are rewarded for interrupting opposition passages of play as well as setting up scores for their own team.

Players who consistently produce positive contributions are rewarded more highly than players with a high volume of stats. As an example, a 20 disposal game by Cyril Rioli where 17 disposals are positive and only one is negative can have the same impact as a 40 disposal game by Dane Swan where 25 are positive and nine are negative.

Can players lose points during games?
Yes. Players can get a negative score in a number of ways, including when they give away free-kicks and also when they turn the ball over. A turnover that results in an opposition score results in the largest negative score.

How is the player ratings system different to the scoring system used in AFL Fantasy and the Champion Data player ratings?
Whereas AFL Fantasy scores simply takes into account how many times a player receives and disposes of the ball, how many scores he registers and whether he wins or gives away free kicks, Official AFL Player Ratings take into account a whole range of other factors. These include where the player was on the field when he received the ball, whether the player was under pressure and whether his disposal advantaged his team or led to a score.

How many players are included on the ratings list?
Only currently listed players are on the list. For this reason, the end-of-season placing for players may be significantly different to their placing at the start of the following year if players above them have retired or been delisted. As soon as a player makes his senior debut, he will begin accumulating points toward his Official AFL Player Rating.  

Are players also rated by position?
Yes. It will be possible to click on our player ratings page and view a list of ruckmen, defenders, forwards and midfielders. Some players may satisfy the criteria for multiple position types, but each player has been assigned a primary position. These classifications are reactive, based on what role a player has performed in recent matches and feedback from AFL club staff. A twice-yearly audit of every listed player will be conducted – one in the middle of the year and one towards the end of the season – but provisional updates may be made for obvious role changes.

Will the algorithm used to determine the Official AFL Player Ratings change in the future?
There will be some slight tweaks. This will be done to ensure the ratings keep up with potential changes to the way the game is played and take full advantage of any new information that is recorded about the game. Any changes will be performed during the off-season and will be fully communicated to the public.

Why are some players rated higher than others I think are better players?
Here are three case studies

Cyril Rioli (forward)
Because of the high value of possession in the forward half of the ground and inside 50, efficient use of the ball forward of centre is highly rewarded. Cyril Rioli's kicking efficiency in the forward half of the ground in 2012 ranked ninth of the 142 players with 100 or more kicks. When Rioli kicked the ball into the forward line he found a mark 31% of the time – ranked third of the top-75 players for inside 50 kicks. Rioli ranked first in the competition for tackles laid inside the forward 50 of players to play five or more games in 2012 and ranked sixth for total pressure applied in the forward half of the same group.

Nic Naitanui (ruckman)
It may be a surprise that Nic Naitanui is clearly the highest-rated ruckman in the League. He finished his 2012 season as the starting ruckman in the All Australian team, polled more Brownlow votes than any other ruckman and more votes in the AFL Coaches Association Champion Player than any other ruckman. Below is a table of seven ruckmen and where they ranked in 2012 in certain stats of the 37 ruckmen to have played five or more games. Naitanui has the best hitout to advantage win percentage, ranks second for contested possessions and third for pressure acts and goals. Excluding uncontested possessions, which gain very few points in Equity Ratings, no other ruckman is in the top-three in more than one category, let alone coming close to Naitanui's four.
 
Player Mt Hitout to Adv. Win % Contested Possessions Uncontested Possessions Pressure Acts Tackles Goals
Nic Naitanui 22 1st 2nd 34th 3rd 9th 3rd
Patrick Ryder 15 4th 9th 5th 12th 18th 2nd
Shane Mumford 17 11th 16th 25th 2nd 1st 8th
Dean Cox 24 7th 11th 1st 30th 31st 1st
Ivan Maric 21 9th 5th 3rd 8th 4th 20th
Sam Jacobs 24 2nd 20th 2nd 29th 32nd 24th
Aaron Sandilands 14 8th 1st 23rd 37th 37th 16th

Daniel Rich (midfielder)
Daniel Rich's long kicking is the feature of his game, having kicked 13 goals from outside 50 in 2012 – more than any other player. He averaged the 14th most metres gained from kicks in the competition and had the fifth best retention rate of the top 15. Over the past two seasons he has averaged 33 metres gained per kick – ranked 12th of any player with 200 or more kicks.