| In sports like Australian Rules football and soccer, teams must
battle to achieve possession of the ball in sufficient space to make
optimal use of it. Ultimately the teams need to score, and to do that
the ball must be brought into the area in front of goal - the place
where the defence usually concentrates on shutting down space and
opportunity time. Coaches would like to quantify the trade-offs between
contested play in good positions and uncontested play in less promising
positions, in order to inform their decision-making about where to
put their players, and when to gamble on sending the ball to a contest
rather than simply maintain possession. To evaluate football strategies,
Champion Data has collected the on-ground locations of all 350,000
possessions and stoppages in the past two seasons of AFL (2004, 2005).
By following each chain of play through to the next score, we can
now reliably estimate the scoreboard "equity" of possessing
the ball at any location, and measure the effect of having sufficient
time to dispose of it effectively. As expected, winning the ball under
physical pressure (through a "hard ball get") is far more
difficult to convert into a score than winning it via a mark. We also
analyse some equity gradients to show how getting the ball 20 metres
closer to goal is much more important in certain areas of the ground
than in others. We conclude by looking at the choices faced by players
in possession wanting to maximise their likelihood of success.
KEY
WORDS: Notational analysis, Australian Rules Football, tactical
coaching.
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