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Evaluating Blocking: Part 2

Stats LessonsJoseph TrinseyComment

In Part 1 of our series on Evaluating Blocking, we noted a few of the challenges that make evaluating blocking difficult:

  1. The blocker doesn’t have full control. On most sets, the hitter can beat the blocker with the right shot. It’s possible to make a good block and still have the hitter kill the ball.

  2. Many attacks never touch the block. At some levels, over half of attacks will touch the block, but at lower levels (such as high school), more than 3/4 of the attacks will go clean past the block. It’s difficult to evaluate the effectiveness of a block when the blocker doesn’t touch the ball.

  3. There are lots of non-terminal blocks. At the NCAA women’s collegiate level, only about half of block touches are stuffs or tools/errors. It’s not always clear whether a “block touch” (that doesn’t result in a point for one team or the other) is a positive or negative play.

  4. It can be difficult to separate the performance of the player from the system they play in.

  5. The standard box score in the USA, the NCAA box score, is mediocre at best at giving you blocking information.

We talked about the last point, and we saw that adding block errors/tools to the equation gives you better information with which to evaluate your blockers.

Teach players that their number-one job as a blocker is to stuff the ball. But the next most important thing is to not give up an easy point by getting tooled! Understanding both sides of this equation makes blockers better.

But what about point #2? Many attacks never touch the block. In this match, Texas defended 112 BYU attacks. BYU made unforced errors on 9 of those balls, and the Texas block touched 50 of them in some way, which means 53 of 112 BYU attempts, or 47%, were untouched by the Texas block. On the other side of the net, BYU defended 90 Texas attacks. 6 were unforced errors and 37 were touched by the BYU block, which means 52% of Texas attempts were untouched by the BYU block.

What do we do about all of these non-touches?

First, let’s look at how I scored them on the GMS Stats app:

BYU Opponent Sideout Screen, GMS Stats App

BYU Opponent Sideout Screen, GMS Stats App

Texas Opponent Sideout Screen, GMS Stats App

Texas Opponent Sideout Screen, GMS Stats App

BYU is on top, and Texas is on the bottom. Both of these screens are displaying our favorite blocking stat: “Stuff to Tool Ratio” as the Blocking Efficiency stat. If you refer to how Volleymetrics graded their blocking in Part 1, you’ll notice two things:

  1. There is a bigger gap between Texas and BYU in my app than in the Volleymetrics grading.

  2. Both teams have a lower ratio in GMS Stats than in Volleymetrics.

Why is that?

The reason for this is that I assigned a Block Error or Dig Error on every opponent kill. I always grade block and defense in this way, and recommend everybody taking statistics on their team to do the same. So instead of 16 Blocking Errors, I gave Texas 18. Instead of 9 Blocking Errors, I gave BYU 15. In some cases, these Blocking Errors are plays where the block did not touch the ball at all, but I assigned them as the primary responsibility for the kill. For example:

In most grading systems, neither of these would register as actions by the blocker. But clearly, the blockers bear responsibility to stop these attacks. While both of these hits could have been dug, they would require a heroic effort by the defender. My judge is that if you had to decide, “which of these players is primarily responsible for that point being allowed,” you would choose a blocker in both instances. We’ll call this grading system, “primary responsibility grading.”

One of the great things about advanced programs like Volleymetrics or DataVolley is that you can drill down deep into things like this. When I was with the USA National Team, we had a system for evaluating Blocking Efficiency that we called, “Expected Attacking %.” In this stat, we had 6 different grades of block touch, including a tag for, “No Touch,” where the hitter hit a ball hard past a blocker and the blocker failed to get a touch on the ball. In this system, the “expected efficiency” of each touch (except stuffing the ball or getting tooled) is always some fraction of a kill; remember that even good touches that slow the attack down are mishandled by defenders sometimes and even poor deflected touches are dug sometimes as well.

Some other coaches might use a 3 or 4-point scale rating for blocking where they assign each touch a value and give the blocker a grade like 1.6 or 2.2 (there’s some other issues with this particular system that we’ll discuss in part 3). We’ll call systems like this or “Expected Attacking %,” “fractional grading.”

This allowed us to get precise values for how a blocker affected an opponent’s ability to score against her. Unfortunately, most high school and club coaches don’t have dedicated statisticians or the budget for advanced statistics software! That’s why I don’t use a fractional system for blocking in the GMS Stats app. A primary responsibility system is easier to keep track of, because blocking touches are only assigned when the rally ends- either with a kill or stuff block.

Sometimes there are judgment calls:

While this is not a straight-down kill, it’s also a difficult play for the defender. Many coaches would be tempted to just call it a “good hit” by the attacker and leave it at that, but I think you’re missing some information. I decided to assign responsibility to the left-back defender. Let me know what you think in the comments section.

In summary, there’s a “Goldilocks Zone,” for most volleyball statistics where getting the right data can get you 90% of the information you need, but getting that last 10% of information requires massive resources. For NCAA and professional teams, that can be a worthwhile expenditure of resources, but most high school and club coaches just need to get the most bang for the buck!

In my opinion, the Goldilocks Zone for blocking is:

Not Enough Info: Only keeping track of stuff blocks.

Too Much Time/Energy: Using a fractional grading system to capture the value of every blocking action.

Just Right: Track stuff blocks and blocking errors, and use a primary responsibility grading system to capture a few additional non-touches that the block was responsible for.

In Part 3 of our series on Evaluating Blocking, we’ll dive deeper into non-terminal block touches and try to find out how much they really matter.