Tag Archives: expected points

Primer – Poseidon ratings

Poseidon ratings are a new team rating system for both the NRL and the Queensland Cup.

For those who don’t have time to read 2000+ words, here’s the short version: the purpose of Poseidon ratings is to assess the offensive and defensive capabilities of rugby league teams in terms of the number of tries they score and concede against the league average. By using these ratings, we can estimate how many tries will be scored/conceded in specific match ups and then use that, with probability distributions, to calculate an expected score, margin and winning probabilities for the match-up.

poseidon

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Spinning the rugby league roulette wheel

The biggest problem I face in trying to work through rugby league analytics is a lack of useful, reliable, easy to source data to analyse. For this post, I had to do it myself.

I recorded 1,000 sets of six from the 2018 season so far, ranging from a Titans-Warriors pre-season game and finishing during the Titans-Bulldogs game in round 15. A thousand may sound like a lot but given there are about 80 sets of six per game, it’s about a dozen games worth of material. We are working with a relatively small sample size and that the probabilities we estimate may not precisely align with reality. If I had the time and patience (a salary could substitute for time and patience), I could go through the entire history of the NRL and do a better job. This site’s motto is “you get what you pay for”.

But today is not about solving problems once and forever. There are a number of ways to solve a given problem and the techniques and data presented here are hopefully what will be a foundation to build upon. This post is about demonstrating that rugby league can be analysed statistically and useful conclusions can be drawn.

rsz_roulette

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