Measuring Team Defence

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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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14 comments

    1. That is the effectiveness of scoring from the chances you have. It says nothing about how many chances you.
      It is a measure of attack after defence, not of defence.

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      1. I’m using D here they way you did above – as the number of defensive opportunities, not the number of digs. Thus, K/D inherently includes the number of chances your create from defense, since K is some fraction of your ATT figure. Ultimately, you want to maximize K/D – your ability to score points in transition. Your ATT/D is part of that, though it fails to account for the quality of the attacks you are able to produce. That’s why I suggest K/D as the ultimate final target metric.

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      2. I got it now. I read ‘that phase’ as ‘break point phase’.
        My objective is to determine the number of chances I have. So some version of this idea is what I am looking for. The effectiveness of the attack is a different part of the puzzle. K/D doesn’t tell me if my defence is good/bad or my transition attack.
        In the same way, I never look at attack efficiency. I always look at all three numbers separately. Efficiency is neat, but it doesn’t tell me anything interesting.

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