Soccer goals, analysis suggests, are scored at different rates throughout the course of matches as teams tire and as, sometimes, one team is forced to press for a goal or chooses to concentrate on defending. Armed with the data provided by Paul from afltables.com, which includes every scoring and end-of-quarter event from every game played between the start of season 2008 and the end of the home-and-away season of 2014, we can investigate whether or not the same is true of AFL scoring.
Firstly, to provide some context, I've summarised the scoring-event data by quarter, which reveals that teams tend to score fewer points in 1st Quarters than in any other quarter because they generate fewer Scoring Shots and convert them into Goals at a lower rate. Scoring in 2nd Quarters is higher than in 1st Quarters mainly because Conversion rates are over 1.5% points better, though there is also a slight increase in Scoring Shot production.
The 3rd and 4th Quarters bring even higher rates of Scoring Shot production and see conversion rates at about the same level as they are in 2nd Quarters. Consequently, average Scoring rises.
In aggregate, an average game produces about 50 Scoring Shots but, a little like soccer, they don't tend to come at exactly the same rate throughout the game. The table below charts the timeline of average Scoring Shot production, grouping the time at which Shots occurred into 20 equally-sized time-slices within each quarter. In a quarter, for example, that runs for 30 minutes (roughly the average historical length of every quarter), each time-slice represents 5% of 30, or 1.5 minutes. Grouping time in this way ensures that each slice represents the same proportion of the total elapsed time of, say, 1st quarters across games with different length 1st quarters.
Since each slice represents 5% of a quarter, if Scoring Shots were produced at a constant rate throughout the quarter, each slice would be expected to contain 5% of the Shots. The y-axis shows the proportion of scoring in a time-slice relative to that 5% expectation. A dot above the 100% line represents a 5% time-slice in which Scoring Shot production was, on average, at higher than the expected rate. A dot below the 100% line represents the opposite.
We can see immediately that Scoring Shot production is depressed in the first time-slice of each quarter, a reflection of the physical reality that each quarter starts with a bounce at the centre of the field. It takes time to transport the ball from there to an area of the field with point-scoring potential. Also, in most quarters, there's an elevated Scoring Shot production level from about the 10% to the 25% mark (ie from about the 3 to 7.5 minute mark in a typical quarter) and a reduction in Scoring Shot production from about the 80% of 85% points (ie for the last 4.5 to 6 minutes of each quarter).
The overall pattern of Goal-scoring is similar to that for Scoring Shot production though Goal-scoring remains at elevated levels for longer at the start of each quarter (after the first 5% is completed), and rates decline more dramatically at the end of quarters.
Behind-scoring, excluding Rushed Behinds, has quite a different trajectory. It is, as for Goal-scoring and for the same reason, depressed for the initial 5% of each quarter, but thereafter is remarkably flat.barely straying from the 100% line marking expected levels for most of the time-slices in most quarters.
In final terms there appears to be a slightly depressed rate of Behind-scoring for about the last 25% of the quarter, with the exception of the last 5% where Behind-scoring rates shoot up, as they do in the final 5% of all other quarters as well. (Note that any scores registered after the siren are included in the final time-slice here and for all other analyses in this post.)
Included below, for completeness' sake only, is the chart for Rushed Behind-scoring. Note that it is subject to much higher levels of variability since the average number of Rushed Behinds per game is very small (4.7, as per the table above).
With the exception mainly of the time-slices at the beginning and end of each quarter, the rates of Goal-scoring and Behind-scoring - and, by implication, Scoring Shot production - are mostly constant across the entirety of all quarters.
Where there are other periods of elevated or depressed Scoring rates, these rarely deviate by more than 5-10% from a constant rate of Scoring.