Student Research | Introducing A New Rating System For World Rugby Union Based On The ELO Rating System: The ELOR (ELO-Rugby)

This excerpt is taken from an MSiA student research blog posting. Each month, students in our program submit original extracurricular research as part of our blog competition. The winner(s) are published to the MSiA Student Research Blog, our program website, and receive a chance to attend an analytics conference of their choice. Visit our blog to see more.

ELOR RATING SYSTEM

Introduction

Ever since I was little, rugby has been my favorite sport. Rugby is still a developing sport in the USA, but the national team has been in every World Cup, but one and is now solidly entrenched as a top 15 team in the world. Rugby rules and scoring are similar to American Football’s, and some players even switch between the two (Nate Ebner, for example, was both an NFL player for the Patriots and a rugby player for the USA Rugby 7’s team). Something I was always fascinated with was how much of an NFL game was quantifiable with stats. You could get favorites, pre-game odds, in-game odds, etc. World Rugby rankings could not do that (except for giving you the ranking from 0 to 100 before the game), and it left me wanting for a more comprehensive ranking system that could be used in more dynamic ways. For example, on October 6th, 2018, New Zealand (the number one team in the world) came back from 17 points down to beat South Africa in just 20 minutes of playing time. In the world of Rugby Union, this kind of result is rare. I was eager for a way to quantify just how surprising this result was. Since the world rugby ranking system has never been used in order to do this, I settled on the ELO rating system, which allows, amongst other things, for in-game win probability adjustments and would be good to evaluate how daunting this comeback really was. Let’s dive right into it.

Background

Dr. Arpad Elo developed ELO in the 1950s to rank chess players. Since then, ELO has most notably been adapted to the National Basketball Association and National Football League by the journalists of the website FiveThirtyEight. A version for world soccer also exists on eloratings.net. I will be looking to develop an ELO Rating for Rugby (ELO-Rugby, or ELOR) and will use NFL ELO Ratings as a reference, for a couple of reasons: a) Rugby Union and American football scoring is relatively similar: seven points for a touchdown / converted try, three points for a field goal / penalty kick (this makes it easier when building the model to look at margin of victory for example and helps in determining a conversion between points and ELO score) and b) NFL teams play between 16 and 19 (if they go all the way to the Super Bowl) games per season, and most major rugby union teams participate in between 10 and 15 games per season. The similarities make the NFL ELO system a good starting point, but some tweaks and changes need to be implemented.

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