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Thursday, December 12, 2002

And the Beat Goes On: Derek Jeter and the State of Fielding Analysis in Sabermetrics - Part 8

In the final installment, Mike wraps up our early Christmas present.

Variations on a Theme: Where Can We Go from Here?

Back when I was a member of my high school’s debate team, I learned that it was important that when listening to an argument, to test the evidence that was presented in support of that argument. There were many times when our worthy opponents would offer arguments based on evidence that when carefully considered and understood in context said something quite different from what they intended it to say. Of course, my teams were never guilty of doing the same thing.

Anyway, that experience taught me to be into a skeptic - or rather, reinforced the natural tendency that I have always had.  Once you leave the realm of statements of fact, and enter the realm of interpretation - especially into the realm of intepretation of baseball performance - everything is open to question. An interpreter of the evidence is always making assumptions about how much weight to give an observation, and what this piece of data really means, and how to account for differences in performance based on the environment in which the performance was accomplished, and balancing the relative value of accomplishments. Some of these assumptions are explicit; most are never clearly stated. But all of them should be tested against the weight of all of the known facts.

So when I heard the variations on this theme:
   

“Every defensive method says Jeter is a terrible fielder.   You simply can’t ignore that much evidence.”

I had to test the methods against the the evidence - because the methods themselves were not evidence, but interpretations of the evidence. I had to discover for myself the extent to which the developers of those methods had interpreted the evidence appropriately, in context.

I first started looking at this at about the time that Baseball Prospectus 2001 came out, and Clay Davenport had totally revamped his DFTs. I was surprised that there had been very little empirical validation of defensive methods against play-by-play data, especially for more recent seasons when we’ve had such data available.  I made efforts to understand the methods that were out there at the time, I looked for underlying unstated assumptions about defensive performance implicit in those methods, and I tested those assumptions against the available play-by-play data.

As I indicated at the start of this series, we have very limited information about the number of opportunities that any defender gets to make a play in the statistical record. Most analysts realize that it is folly to attempt to evaluate a defender based on his successes and a partial record of his failures, and most analysts also realize that hits in the field of play result (to some degree) from a defensive failure. For that reason , every defensive method that is not based on play-by-play data makes assumptions about the distribution of opportunities among fielders. Yet even with those assumptions, methods not based on play-by-play data reward players who get more opportunities, and penalize players who get fewer opportunities - even those methods like the DFTs and CAD that use PBP data to help estimate the distribution of opportunities. Every ball fielded by someone else will drive a fielder’s defensive rating down in most systems. In the case of the Yankees from 1998-2000, the ball-in-play distribution and the probable alignment of the fielders in the face of that distribution combine to limit the number of opportunities that Derek Jeter has to make plays - and make it nearly impossible for Jeter to rank highly in those methods that are based on traditional defensive statistics.

The one (more or less) open-source method based on PBP data that we do have - MGL’s version of UZR - concludes that Jeter isn’t all that bad a fielder, at least for the 1998-2000 period covered by my analysis. While UZR is not problem-free, it does eliminate most of the guesswork about fielder opportunities, being based on calculated percentages of balls fielded by a defender in an area of the field. The UZR model can be tweaked to allow for more dynamic allocations of fielder responsibility - perhaps by modeling various ball distributions and positioning fielders in that distribution in such a way as to maximize the probability that a ball in play will be fielded by someone, and then evaluating fielder coverage responsibilities within those areas based on a version of Don Malcolm’s force-and-distance model. Such an approach should allow us to define the extent to which fielder percentages in different zones should be expected to vary based on the BIP distribution.

That still leaves the problem of developing better estimators for fielder opportunities in methods not based on PBP data, since we do not have detailed PBP data for most of MLB history. To do this, we need to try to take advantage of the PBP data that we do have (including the 20 years worth of data that has been released through Retrosheet) to figure out better ways to estimate opportunities from what we have when we don’t have PBP data.

Most of the adjustments for BIP distribution have been made on either the total number of balls in play or (in Win Shares) on the successful plays. But perhaps we can approach this from a different angle. We already know the direction of the outs in play - we get those from the assist totals for the infielders and the putout totals for the outfielders. Thus we really only have to try to estimate the distribution of hits in play. We can estimate the number of singles, doubles, and triples per team given the rest of the team stats - one way to do this is to take Bill James’s component ERA formula and work backwards to get an estimated number of total bases allowed based on the team ERA, then divide into singles, doubles, and triples based on average percentages allowed. Once we have singles, we should be able to estimate the percentage of those that are ground balls (since we can estimate the GB/FB distribution for a team). The assist totals for the infielders should help us develop estimators for the direction of ground ball singles (as will the L/R pitching distribution, since most GBs are pulled). The idea is to take advantage of everything that we know from the basic data, and combine that with inferences that we draw from the PBP data - if we knew from the PBP data that singles fell in about the same distribution as the outs fall, and that they are distributed among fielders in about the same proportion as some combination of the left side/right side assists and the LH/RH pitching distribution - we could devise a range rating similar to that in CAD. We’ve tried to do that based on total BIP, but it might make more sense to do that based on (assists+estimated hits in play). That’s one way to approach the problem - and given the number of comments that have already come forward on this series of articles, I have no doubt that those of you who have worked all the way through this analysis with me have your own ideas as well. In any event, we should be trying to work back and forth from the PBP data to the method and validate whatever conclusions we draw back against the PBP data. No one should undertake defensive analysis without starting from players for whom there is PBP data, because there is no other way to validate whatever assertions you make about opportunities.

I selected Derek Jeter for this analysis because I found it hard to accept the extent to which the analytical conclusions were at odds with the perception among baseball men. I didn’t doubt that Jeter was overrated as a defender, mind you, but having looked at STATS zone data for 1999 and 2000, and knowing that Jeter was seeing very few balls in his zone, I began to wonder if it weren’t the methods themselves that were at fault. After investigation, I’m convinced that the non-PBP methods are systematically downgrading Jeter because they fail to account for his lack of opportunities, and until we do a better job of leveraging what we know or can estimate from the PBP data into the non-PBP based methods, we will always have to remember that a rating could be as much the result of opportunity as it is of fielding skill.

In writing this series of articles, I hoped that, more than anything else, the Primer readers would provide thoughtful feedback and commentary. That hope has been realized in spades. I appreciate the amount of time and effort that you have taken to read and react to these articles, and I hope that you will continue to do that in response to this article and to anything else the Primer authors write. We’ve got a great group of writers and an even better group of readers. Thanks!!

Mike Emeigh Posted: December 12, 2002 at 06:00 AM | 9 comment(s) Login to Bookmark
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   1. tangotiger Posted: December 12, 2002 at 02:09 AM (#607554)
Yes, great stuff.

I especially applaud this line
The idea is to take advantage of everything that we know from the basic data, and combine that with inferences that we draw from the PBP data
This is what we should be doing (for historical purposes).

As for UZR, look in the "Articles" section of Primer for anything written by Lichtman.
   2. Charles Saeger Posted: December 12, 2002 at 02:09 AM (#607555)
The likely CAD fix for this, which I shall make when we have more data:

* Use league assist/first base putout numbers to give a normal scatter of outs.

* Set those numbers to the team infield outs, so first basemen have the same percent of outs, second basemen have the same percent of outs and so on.

* Fix for left/right skew.

* Using skews we made from looking at PbP numbers, set hits for each fielder. For instance, we may set the shortstop hit percent to shortstop assists, plus one quarter of second baseman assists, plus one sixth of third baseman assists, as a percent of the team total of all these Frankenstats we made. We do this with the league numbers.

* Do this again with the team numbers.

* Somehow balance the two numbers.

Thus, we look at two numbers -- one of what we would think the team hit skew should be from league numbers and the handedness of its pitching staff (or opposing batter handedness), and one of how the outs fell against this one team.

As for doubles and triples, the fix in the end will be to look at old box scores and find out how many doubles and triples batters hit against each team. We can make formulae until this is done.
   3. bob mong Posted: December 12, 2002 at 02:09 AM (#607568)
Great series of articles, Mike. Loved 'em. And I heartily agree that any defensive-evaluation method should be verified, whenever possible, by empirical data (i.e., play-by-play data).
   4. The Original Gary Posted: December 13, 2002 at 02:09 AM (#607578)
I too voted for Lowe and Pedro over Zito (although I am swayed somewhat by the superior hitters faced by Zito). I thought Lowe was better for a few reasons - (1) 23 more IP, and (2) Lowe could have pitched more innings. While the Red Sox often pulled Lowe after 5 because they were up by a bunch, they often, on the other hand, pulled Pedro after 5 or 6, particularly earlier in the season, with a 1 or two run lead simply because they didn't think he could pitch any further. While I don't think Lowe necessarily deserves extra points for better run support, the fact of the matter is that, had the two been reversed, Lowe could have and would have pitched more innings, but Pedro would have pitched the same # or less. In other words, Pedro's fragility required extra contributions on the part of his teammates, so his wins, while impressive, required slightly more "assistance".
   5. Mike Emeigh Posted: December 13, 2002 at 02:09 AM (#607580)
Mike, do you know the reasons for his lack of opportunities?

As I noted earlier in this series, the Yankees have an odd BIP distribution, skewed toward the holes on either side of the infield and away from the middle of the diamond. The PBP data suggests strongly that the Yankee 3Bs are covering the SS hole, and the 2Bs are covering the 2B hole. That leaves Jeter, most likely, shading toward the middle of the diamond - where there just aren't that many balls put into play.

I don't know why the Yankees had this odd distribution. I've noted elsewhere that pitchers generally don't have much to do with the distribution of BIP against them, but the ball distribution against the Yankees is defenitely skewed toward the right side much more than one might expect given the distribution of hitters facing them.

One can speculate that the Yankees might be well aware of Jeter's defensive deficiencies and are (a) positioning their defense and (b) charting their pitchers' patterns to reduce the likelihood that balls will be hit to Jeter. I certainly can't rule out that possibility, although the available evidence suggests that pitchers can not "pitch to the defense" consistently.

-- MWE
   6. tangotiger Posted: December 13, 2002 at 02:09 AM (#607584)
Mike, a couple of breakdowns. Is there maybe one really oddball pitcher in the lot that skews the whole thing?

Is there a difference between Yankee stadium and other stadiums for Jeter and for his opponents?

Finally, is it only the Yankees, or do other teams also have weird distributions?

Great job again!
   7. Mike Emeigh Posted: December 14, 2002 at 02:10 AM (#607595)
Mike, a couple of breakdowns. Is there maybe one really oddball pitcher in the lot that skews the whole thing?

Is there a difference between Yankee stadium and other stadiums for Jeter and for his opponents?

Finally, is it only the Yankees, or do other teams also have weird distributions?


When I looked at the breakdowns for the Yankees, the only notable effect was for RH-hitters against the Yankee pitchers. LH-hitters had a more or less normal BIP distribution. There wasn't any one pitcher that stood out particularly, nor was there a home/away difference.

The one other notable odd distribution occurs in Fenway Park, where there are more balls hit to the left side then one might otherwise expect. That's likely to be related to the Green Monster. Ballparks with odd features that shorten a dimension to make it significantly less symmetric - Fenway, Minute Maid w/ the Crawford boxes, OP@CY with the RF scoreboard - appear to have some effect on the BIP distribution.

-- MWE
   8. MGL Posted: December 16, 2002 at 02:10 AM (#607612)
As I've mentioned before, I am updating the methodology for UZR. It should be real good!

It should be ready before the end of January. I'll write an article describing the new methodology and present the results for at least the last 3 years (00-02).

At around the same time I'll present a revised version of Superlwts, including the new UZR's, as well as a description of all the Slwts categories...
   9. Silver King Posted: December 17, 2002 at 02:10 AM (#607638)
Woo!

And hey, pre-2000 will be mega-welcome too, then or eventually.

Mike, fascinating stuff, got other big guns percolating. Thanks!

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