Addressing opposition quality in rugby league performance
Clean Break When a player breaks through the defensive line. Performance indicators were determined by the system implemented in Sportscode and transferred into a Microsoft Excel (Microsoft Inc., Redmond, Washington) to apply the profiling technique described in section 2. The indicator of team quality used was league points accumulated at the end of the season. The relative quality between two teams within a match was, therefore, the difference between their league table points. The absolute correlations for possession time (r=.503), clean breaks (r=.517), attacking errors (r=.521), completed set within own 40m (r=.488) and tries (r=.661) were high enough for a regression model to be produced for each in terms of relative quality (RQ). In each case an equation of the form PIExp = a + b x RQ was produced for the expected value of the performance indicator. The residual values for a performance indicator had a mean of 0.0 and a standard deviation, SDRes, that could be used to produce a z-score for an observed value of a performance indicator, PIObs (z = (PIObs – PIExp) / SDRes). The percentage evaluation score, %ES was calculated using the probability distribution of the standard normal distribution; %ES = 100 x NORMDIST(z). 4. RESULTS Figure 1 shows the relationship between possession time, PT, and relative quality, RQ. The regression line represents the expected value given the relative quality
between the two teams within a match. Any points above the line are where a team had more possession than expected given the quality of opposition and any points below the line are where a team had less possession than expected given the quality of opposition.