Introducing True Kicker - A New Metric to Evaluate Goal Kickers in the NRL
Traditionally Goal Kickers in the NRL have been ranked according to their conversion success rate.
However, we know not every kick at goal in the NRL is created equal – an attempt for goal from the sideline is much more difficult than a kick from right in front of the posts. This means evaluating Goal Kickers based solely on conversion success rate may not paint a true picture of a kicker's underlying performance.
Introducing the brand new True Kicker Rating system. Developed by Stats Insider, alongside Stats Perform, the True Kicker will equip fans with a better tool to analyse goal kicking in the NRL. An article about True Kicker was also published by NRL.com, so if you’ve caught a glimpse of that some of the below may be familiar.
So, what is True Kicker?
True Kicker Ratings are a different way of ranking goal kickers in the NRL. In a nutshell, they tell us how many points a player's goal kicking has earned (or cost) their team, over a set period of time, compared to the NRL average kicker.
Under the True Kicker Rating System, each attempt at goal is assigned a difficulty level based largely on where the kick is taken from on the field.
Players are then given a score for each kick based on the difficulty level of the kick, and whether or not the kick is successful. The score corresponds with how many ‘extra points’ that particular kick earned their team compared to the NRL average kicking success rate from that particular location. Thus, scores for individual kicks can be positive (where the attempt is successful) or negative (where the attempt is unsuccessful) and range from +2 to -2.
This is where True Kicker differs from other goal kicking statistics such as conversion success rate – it takes into account not only whether a kick was successful, but also the difficulty of that kick.
This means a player who kicks a goal from the sideline will receive a higher score than a player who kicks a goal from right in front of the posts. Similarly, a player who misses a kick from right in front will be penalised harder than a player who misses a kick from the sideline.
How is the difficulty of each kick calculated?
Using historical data, a benchmark is assigned to each kick that represents how often we would expect the NRL average kicker to kick a goal from that particular location.
Benchmarks typically become lower as the location of a kick moves away from the posts (in distance, and in angle from the goal). The lower the benchmark, the more difficult the attempt at goal.
How are True Kicker Scores Assigned for Each Kick?
If a kick is assigned a benchmark of 60%, that means we would expect the NRL average kicker to nail that kick 60 times if they were to have 100 shots.
If a player were to kick that particular goal, they would score +0.8 under the True Kicker Rating system, being the 2 points scored minus the average kicker’s expected points from that kick (2*0.6 = 1.2). Conversely, if a player were to miss that goal, they would score -1.2 (being the 0 points scored, minus the average kicker’s expected points from that kick) – a negative contribution to their team.
How can True Kicker Ratings be used?
A player’s ‘kick by kick’ scores can be added together to produce an overall score which broadly represents how many extra points they have gained (or lost) for their team above (or below) the NRL average goal kicker. This is also referred to as a player's True Kicker Score.
A score of zero indicates a player has done exactly what we’d expect from the average goal kicker in the NRL, based on the kicks they have taken. A positive score indicates a player has done better than the NRL average kicker and a negative score indicates a player has done worse than what we’d expect from the NRL average kicker.
2017-2019 Overall Leaderboard - All Players
Overall True Kicker Score
*All Numbers include data from the 2017, 2018 and 2019 seasons. Players must have attempted a minimum of 60 shots at goal in that period to qualify for the lists.
So for example an overall score of +22.4 for Nathan Cleary means his goal kicking has earned his team 22.4 more points than we would have expected over the 3 year period. Contrast this with a score of, for example, -17.5, which would mean that player’s goal kicking has cost his team 17.5 points over the same period.
One thing to be aware of is the player on top of the overall leaderboard is not necessarily the best ‘pound for pound’ kicker in the NRL - because a player’s overall score is calculated by adding together the scores for all their individual kicks it will naturally lean towards good kickers who have taken more shots at goal. However, it is a really good way to see just how many points a player’s goal kicking has contributed to their team over a given period of time and tends to reward consistent performance over that period.
Per Kick Ratings
While the overall leaderboard has a number of benefits, it can also be useful to look at the True Kicker Ratings on a ‘per kick’ basis- which can work well as a ‘pound for pound’ measure when players have taken a lot of shots at goal.
One way we can do this is by looking at a player’s ‘Actual v Expected’ Goal Kicking Success rate. This is also referred to as True Kicker Differential.
The kick by kick, difficulty-adjusted-rating-system which has been adopted,allows us to calculate ‘what we would expect’ the NRL average kicker's goal kicking success rate (penalty goals + conversions) to be based on all the individual kicks a certain player has attempted.
By comparing this to that player’s ‘actual’ goal kicking success rate we can calculate how much they have exceeded (or fallen below) expectation. This number is presented in the form of a percentage and represents ‘how much better or worse a player’s conversion success rate is than we would expect it to be based on the kicks they have taken’.
2017-2019 Per Kick Leaderboard - All Players
True Kicker Differential
*min 60 shots at goal
One thing to keep in mind when using per kick ratings is they can be subject to more volatility and change, particularly when players have taken relatively few shots at goals.
This volatility in part can be driven by elements of luck – when a player has had only a few attempts it’s possible they got lucky (or unlucky) in kicking (or missing) some of those goals which in turn has an impact on their True Kicker Differential. However, it’s harder to get lucky (or unlucky) over a larger number of kicks which is why we expect to get a clearer picture on players as they attempt more shots at goal – and also why we have placed a minimum 60 kick threshold to qualify for the list above.
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