Objective Truth in Defensive Analysis

[RVAbird]

Colin Wyers is quickly becoming a favorite of mine over at BP, despite a (sometimes entertainingly) smug attitude. Lots of people are up in arms about another Jeter gold glove, but it's really a push for analysts to get introspective and honest about our "advanced" assessment of defense.

Some excerpts for non-subscribers:

Last week, I talked about the idea that sabermetrics is (in part) the scientific study of baseball. I don’t think that all of sabermetrics is science, of course, but I think that’s a large part of it. And I think that more than anything else, a sabermetrics that is manifestly anti-scientific ceases to be sabermetrics at all.

One of the key requirements for scientific research is reproducibility—the idea that independent observers can come to the same conclusions as the original researchers. The reproducible parts of fielding analysis are things like DER—measures that tabulate plays made and balls in play, objective facts that anyone can derive using scorekeeping methods that Henry Chadwick came up with in the 1870s. Modern advancement in fielding analysis relies on estimates of expected outs from batted ball data.

And that data has proven not to be reproducible on two counts—different data providers cannot reproduce the same estimates of where a ball landed and how it got there, and different analysts using the same batted-ball data cannot reproduce the same estimates of expected outs.

And so if we want to know why people don’t trust what we’ve come to call “advanced” fielding analysis, it’s really because we haven’t given them a reason to trust it. And that’s because of a fundamental abandonment of what makes sabermetrics compelling—the search for objective truth. For a time we stopped doing science when it comes to fielding analysis, and instead have been doing baseball alchemy—trying to transmute lead into Gold Gloves.

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Link

[Frobby]

It is very true. By the way, what is the status of the cameras they were going to install at every stadium to measure the speed, angle etc. of every batted ball? I thought that was going into effect this season and that we'd see some new analyses that might be more accurate than past attempts.

[Arthur_Bryant]

It is very true. By the way, what is the status of the cameras they were going to install at every stadium to measure the speed, angle etc. of every batted ball? I thought that was going into effect this season and that we'd see some new analyses that might be more accurate than past attempts.

Here's an excellent article from the SF Chronicle this past April, running down the system(s) and the nuts and bolts. Apparently only AT&T Park had the full system installed this year, but all MLB stadiums should be up and running in 2011.

There are actually two different systems. Hitf/x uses the existing Pitchf/x cameras to track batted balls through their field of view--basically until the edge of the outfield. I guess that data exists but isn't widely disseminated, and is labor-intensive to sift.

But the big step forward is Fieldf/x, which should capture the whole field, including movements of the fielders.

Here's a blog report from late August in BP on the 2010 Pitchf/x Summit which contains some nice nuggets, including the fact that the weight of 40,000 people in the stands will actually distort the calibration of the Fieldf/x cameras.

And for the truly hardcore, here are videos of presentations at the Summit itself.

[Frobby]

Here's an excellent article from the SF Chronicle this past April, running down the system(s) and the nuts and bolts. Apparently only AT&T Park had the full system installed this year, but all MLB stadiums should be up and running in 2011.

There are actually two different systems. Hitf/x uses the existing Pitchf/x cameras to track batted balls through their field of view--basically until the edge of the outfield. I guess that data exists but isn't widely disseminated, and is labor-intensive to sift.

But the big step forward is Fieldf/x, which should capture the whole field, including movements of the fielders.

Here's a blog report from late August in BP on the 2010 Pitchf/x Summit which contains some nice nuggets, including the fact that the weight of 40,000 people in the stands will actually distort the calibration of the Fieldf/x cameras.

And for the truly hardcore, here are videos of presentations at the Summit itself.

Thanks. This looks like it could lead to a lot of enlightenment about fielding.