Development of an expected possession value model to analyse team attacking performances in rugby league

TL;DR

This paper introduces an expected possession value (EPV) model for analyzing rugby league attacking performance, demonstrating that a simplified 19-zone model effectively captures team performance and allows for meaningful comparisons.

Contribution

The study develops and validates a novel EPV framework using Markov Chains and zone-based analysis, highlighting the effectiveness of a 19-zone model for evaluating attacking performance.

Findings

EPV-19 provides consistent performance evaluation across matches.

The 19-zone model shows high reproducibility and simplicity.

EPV-77 and EPV-308 are less reproducible and more variable.

Abstract

This study aimed to provide a framework to evaluate team attacking performances in rugby league using 59,233 plays from 180 Super League matches via expected possession value (EPV) models. The EPV-308 split the pitch into 308 5m x 5m zones, the EPV-77 split the pitch into 77 10m x 10m zones and the EPV-19 split the pitch in 19 zones of variable size dependent on the total zone value generated during a match. Attacking possessions were considered as Markov Chains, allowing the value of each zone visited to be estimated based on the outcome of the possession. The Kullback-Leibler Divergence was used to evaluate the reproducibility of the value generated from each zone (the reward distribution) by teams between matches. The EPV-308 had the greatest variability and lowest reproducibility, compared to EPV-77 and EPV-19. When six previous matches were considered, the team's subsequent match attacking performances had a similar reward distribution for EPV-19, EPV-77 and EPV-308 on 95 +/- 4%, 51 +/- 12% and 0 +/- 0% of occasions. This study supports the use of EPV-19 to evaluate team attacking performance in rugby league and provides a simple framework through which attacking performances can be compared between teams.