I have never liked the ‘traditional’ defensive statistics. A simple count of the number of digs has no meaning, reliant as it is on so many things. The next obvious ‘solution’ is a percentage of dig attempts, however that leads to the difficulty of defining an attempt. While for individual coaches it is possible to create a meaningful statistic, establishing consistency across coaches is difficult.
To come up with a measure of how my defence worked that was useful to me, I started with first principles. What do I want to know? Some coaches consider good defence anything that keeps the ball in play. I am not one of those coaches. The object of defence is to create attacking opportunities. For me, a good defensive action is one that leads to an attack. So we can start with the number of attacks in transition after serve as our idea of a successful defensive action.
Next I came up against the familiar problem of what to use as denominator. As I wanted to look at other teams as well as my own, and I couldn’t know for sure how they might define a dig attempt, using dig attempts was not an option. I thought of using serves as the base, but that would include aces and service errors which don’t belong. Finally, I settled on a ‘defensive opportunity’ being all reception attacks that are not blocked or direct errors.
So my statistic is ATT/D, defined as attacks per defensive opportunity.
There are obvious holes in this. You can have more than one attack from a single defensive opportunity, and spikes that are hit off the block count as a defensive opportunity, even if they aren’t, to name just two. Ultimately, I decided that given that my objective was to be able to make inferences about defence in matches that I couldn’t rely on the definition of a dig, ATT/D is close enough for me to be able to say something.
I have been following this for two seasons now, and I feel confident that it shows me how my team is defending. I know that anything in the 0.40 – 0.49 range is ok. If we reach 0.50 we are defending well and if I see a 0.3 number we are bad. If I combine this with transition attack percentage after serve, I can see very well why our break point percentage is whatever it is.
So there you have it…
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