Tag Archives: nrl

A glance at the NRL with Poseidon ratings

If you read my tips for round 1, you would have seen the Poseidon rating making an appearance. The purpose of the Poseidon rating system is to look at each team’s offensive and defensive capabilities separately, as well as their home and away performance, to see if their winning record is concealing strengths or weaknesses.

The underlying principle is quite simple. We look at how many tries a team scores, at home and away, and how many they conceded, similarly at home and away, and see how that stacks up against the league average over the previous twenty-four rounds.

The league average moves over time. In 2013, the home team scored 3.9 tries on average and the away team 3.2. In 2018, those numbers had changed to 3.6 and 3.1 respectively. While 0.3 tries per game may not seem like much, over a 192 game regular season schedule, that’s 57 tries that have gone missing, or about 316 points, just for the home teams.

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NRL Tips – Round 1, 2019

But first, a refresher

This year I’m going to be providing tips for each round of the NRL and the ISC using four mathematical rating systems. None of the four metrics rely on subjective human assessments and instead, each rating system takes in cold, hard numbers and spits out tips.

While each tool has a useful predictive track record (some are better than others), they are unlikely to outperform the best human tipsters. However, the systems are also not subject to the cognitive biases that people naturally develop and can offer insights that might otherwise be overlooked.

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Who has the softest NRL draw in 2019?

The current format of the NRL doesn’t allow for each team to play each other twice. Doing that would mean extending the season by another six weeks and, even if they players were up for that (which they are not), as an armchair analyst, I don’t think I could cope.

This means that not every team’s schedule is the same. For twenty-four games, each teams plays each other once and plays a second game against nine other teams. The NRL has no particular interest in trying to provide the mythical “balanced schedule” that would be fair for all teams and prefers to use the opportunity to use a doubling up of rivalry games to generate commercial returns.

This might seem grossly unfair, especially if your team has to play the premiers twice, but it is what it is. What I’m interested in looking at this week is how slanted the schedules are and who will have an easier time of the 2019 NRL season and who will have to do it the hard way.

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A deep dive for each team’s 2019 NRL season

With the first Maori versus Indigenous All-stars game and another edition of the World Club Challenge in the history books, our attention turns to the NRL season ahead.

As with last year, I’m going to do a SWOP – Strength, Weakness, Opportunity and Prospect – analysis for each team. My general philosophy for judging a team’s prospects is that where a team finishes on the ladder the previous year is a more or less accurate reflection of their level, give or take a win or two. If no changes are made, we should see a similar performance if the season was repeated. There are exceptions, e.g. the Raiders pathological inability to close out a game should be relatively easy to fix and the Knights’ managed maybe two convincing wins in 2018 but still finished eleventh, but broadly, if a team finishes with seven wins and they hope to improve to thirteen and make the finals, then we should look at what significant changes have been made in order to make that leap up the table.

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Primer – PPG and WARG

Turns out that StatScore didn’t pan out the way I had hoped. There were some conceptual errors but the biggest was that I wanted a measure of rate and a measure of volume and you can’t have one statistic that does both. It’s like having one number that meaningfully states that a boxer is both the best in the world pound-for-pound but also the best boxer in the world who can beat anyone irrespective of weight classes. The world doesn’t work like that. As a result, there was some okay, but not great, player analysis. Unfortunately, the creation of a new tool requires that you use it for a while on new scenarios in order to evaluate it’s usefulness. Sometimes it doesn’t pan out as well as you would have hoped.

Also, the name sucked.

So I went back to the drawing board. There were some salvageable concepts from StatScore that have been repackaged, with corrections made for some fundamental mistakes, and repurposed into new player rating systems: PPG and WARG.

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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.

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