Evolution of rule changes and coaching tactics in Australian Football: impact on game speed, structure and injury patterns
Video recordings of VFL/AFL games were obtained from 1961 to the 2010 premiership season. A series of both finals games [n=9] and premiership season games [n=129] were reviewed, most covering the period 2000-2010. Information on AFL injury rates were obtained from annually published injury reports produced by the AFL Medical Officer’s Association (Orchard and Seward, 2011). These have been produced every year for the past 19 years. A third independent dataset was also used (Wisbey et al., 2010). This dataset on player movement is based on GPS-tracking and contains six years of data collection. Annual reports are published providing information on player distances, speed breakdowns and time on the field. Other statistical information has also been gathered from Champion Data (www.championdata.com), the official statistician of the AFL. 3. RESULTS 3.1 Game speed There has been a significant increase in play speed in the AFL over recent decades as illustrated in Figure 1. Since 1961 play speed has approximately doubled. 3.2 Play time Play time is the proportion of the game that involves players competing for the ball. That is, when the umpire has not called a stoppage period. The percentage of the game that was coded as play time across the period 1961-2010 is illustrated in Figure 2. It is clear that the general trend for AF is a decrease across the period up to the early 2000s. In more recent seasons there has been an obvious and dramatic increase in the proportion of play time for AFL. 3.3 Play and stop periods Figure 3 shows play period durations were gradually decreasing over the period 1961-1999. Since that time, play period duration has been increasing. The average stop period duration increased up to about 2005 and then declined dramatically thereafter. Interchange rates increased in an accelerated pattern from the early 2000s, as shown in Figure 4. From the first year that interchanging players was
allowed in 1978, the use of the interchange as a coaching tactic was rare and interchange rates remained low for over two decades.