Inside DER

David Pinto started publishing his fielding stats this week (here’s a link to his second base rankings). David obviously doesn’t have a background in marketing; he calls his stat the Probabilistic Model of Range (or PMR). But it’s way cool anyway because…

1. It’s based on batted-ball types, speed and detailed “vectors” (sort of like zones) for every batted ball, and
2. It’s free, though David asks for (and deserves) donations for his great blog.

He’s in the process of posting his rankings for each position, so be sure to check his blog regularly.

Most advanced fielding systems, like UZR and David Gassko’s Range, compare a fielder to his peers that same year. But PMR compares each fielder against his peers over four years, which leads to some interesting conclusions. For instance, Pinto’s findings suggest that fielders did a better job in 2005 than in 2004. Unfortunately, there appear to be a few data consistency issues, making that conclusion less than certain.

Still, I thought it might be fun to look at this phenomenon a little bit as it applies to individual pitchers. So I pulled the batted-ball results of all pitchers who faced at least 500 batters in each of the last three years, just to see what happened to their batted balls. The highest Defense Efficiency Ratio (DER—percent of balls successfully fielded for outs) I found was Al Leiter’s in 2004 (.760) and the lowest was Sidney Ponson’s in 2005 (.650). A difference of .180 is a wide swing, but a fairly typical one. Here’s a link to all qualified pitchers in 2005, top to bottom, in DER.

Batted-ball types play a role here. Not surprisingly, pitchers who give up more line drives have lower DERs and those who have more infield flies have higher DERs. But the thing is, at least for this bunch of pitchers (2003-2005), batted-ball types weren’t that important. The R-squared between batted-ball types and DER was only .10. That means that only 10% of the difference in pitcher DER could be explained by the types of batted balls they allowed. The other 90%? Well…

What really matters is what happens to a batted ball after it’s hit, regardless of whether it’s a ground ball, fly ball or line drive. And there can be some big differences between pitchers in a given year. Take the simple ground ball. In general, ground balls are fielded for outs about 75% of the time. But, as they say, “results vary by pitcher and year.” Take a look at the pitchers who had the highest ground ball out percentages in the last three years:

 Year  Last        First       Team       Grnd Out %
 2003 Ortiz       Russ        Braves        83.5%
 2004 Lima        Jose        Dodgers       82.6%
 2003 Lewis       Colby       Rangers       82.0%
 2005 Martinez    Pedro       Mets          81.9%
 2003 Zambrano    Victor      Devil Ray     81.7%
 2003 Day         Steven      Expos         81.4%
 2005 Zito        Barry       Athletics     81.3%
 2005 Carpenter   Chris       Cardinals     81.1%
 2005 Pettitte    Andy        Astros        81.1%
 2005 Carrasco    Daniel      Royals        80.8%

Russ Ortiz in 2003? Jose Lima in 2004? Now you know why those guys looked so good for such a short time. More of their ground balls were outs. Conversely, here’s a list of pitchers whose ground balls were fielded for outs the fewest times in a given year:

 Year Last        First       Team       Grnd Out %
 2004 Santos      Victor      Brewers       63.1%
 2004 Prior       Mark        Cubs          65.8%
 2003 Leiter      Al          Mets          66.5%
 2005 Ponson      Sidney      Orioles       67.2%
 2004 Bedard      Erik        Orioles       67.3%
 2004 Acevedo     Jose        Reds          67.3%
 2005 Capuano     Christopher Brewers       68.6%
 2005 Kazmir      Scott       Devil Ray     68.6%
 2004 Lohse       Kyle        Twins         68.6%
 2003 Dempster    Ryan        Reds          68.8%

There was a 20-point difference in groundball outs between Russ Ortiz in 2003 and Victor Santos in 2004. That’s, how do you say, a lot. The number two guy from the bottom is Mark Prior in 2004, whose ground balls have consistently been fielded for outs at lower rates each of the last four years. The number three guy from the bottom is Al Leiter in 2003, one year prior to his .760 DER in 2004 (when his Grnd Out% was 77.3%, over 10 points higher).

Systems like PMR help us understand how much of the variance between pitchers is due to their fielders. There is also some evidence that a few pitchers legitimately impact the fieldability of their ground balls (like Prior or Jon Garland). But most variances are just random, as in Leiter’s and Santos’s cases. Take a look at Santos’s batted-ball table (defined here), particularly the difference in net run value per ground ball between 2004 and 2005.

Santos, Victor

Net Runs per Ball % of Batted Balls %/OF %/PA Total Net Runs
BFP OF LD GB OF% LD% GB% HR K BB OF LD GB IF NIP Tot R/G
2002 140 -0.06 0.46 0.02 25% 31% 38% 12% 18% 16% -1.3 12.9 0.8 -0.5 -0.5 11.2 3.0
2003 117 0.00 0.41 -0.22 25% 31% 41% 13% 13% 15% -0.1 10.8 -7.4 -0.5 0.9 3.5 1.1
2004 684 0.00 0.33 0.01 36% 18% 40% 9% 17% 9% 0.9 29.3 1.0 -7.0 -13.3 10.5 0.6
2005 639 0.04 0.30 -0.08 34% 23% 41% 12% 14% 10% 7.3 32.7 -15.3 -2.3 -5.9 16.0 1.0
Avg. 395 0.01 0.34 -0.04 33% 22% 40% 11% 15% 11% 1.2 17.9 -4.2 -2.3 -6.8 5.3 0.5
vs. MLB -0.02 -0.02 0.06 2% 1% -3% 0% -1% 1% -1.9 -3.1 8.3 0.6 0.5

As you can see, the run value of his ground balls improved (went down) nearly a 10th of a run in 2005, because more of them were fielded for outs.

Next I looked at how many “non-ground balls” were fielded for outs. I combined outfield flies and line drives because there are some questions about the consistent categorization of those (as you can see in some of the PMR comments). Let’s call all outfield flies and line drives “airballs” just for fun. Here is a list of those pitchers whose air balls were fielded for outs most often (not including home runs in the denominator).

  Year   Last        First     Team          Air Out %
  2003  Franklin    Ryan      Mariners         72.7%
  2004  Gobble      Jimmy     Royals           71.5%
  2005  Elarton     Scott     Indians          70.6%
  2004  Cabrera     Daniel    Orioles          70.4%
  2005  Blanton     Joseph    Athletics        70.1%
  2004  Santana     Johan     Twins            69.5%
  2004  Milton      Eric      Phillies         69.5%
  2003  Zito        Barry     Athletics        69.1%
  2005  Lee         Cliff     Indians          69.1%
  2005  Contreras   Jose      White Sox        68.9%

Ideally, I would park-adjust these figures because ballparks can have an impact on flyball out percentages. But this isn’t really a “research” article, and I just don’t feel like it. (Start your angry e-mails now!) I’d rather just move on to the list of pitchers whose outfield flies were caught least often. Check out Derek Lowe’s 2004:

  Year   Last        First     Team          Air Out %
  2004  Lowe        Derek     Red Sox          44.9%
  2003  Brown       Kevin     Dodgers          48.7%
  2004  Webb        Brandon   Diamondbacks     49.0%
  2003  Cook        Aaron     Rockies          49.2%
  2003  Lewis       Colby     Rangers          50.9%
  2005  Webb        Brandon   Diamondbacks     51.2%
  2005  Carrasco    Daniel    Royals           51.2%
  2003  Westbrook   Jake      Indians          51.5%
  2003  Rusch       Glendon   Brewers          51.6%
  2003  Day         Steven    Expos            52.4%

There is almost a 30-point swing from the highest to the lowest airball out percentages. In fact, fewer than half of Lowe’s air balls were caught for outs! Now, some of this variance is definitely caused by giving up more line drives, so let’s look at Lowe’s line drives and outfield flies in his batted-ball table:

Lowe, Derek

Net Runs per Ball % of Batted Balls %/OF %/PA Total Net Runs
BFP OF LD GB OF% LD% GB% HR K BB OF LD GB IF NIP Tot R/G
2002 854 -0.02 0.36 -0.15 18% 13% 67% 9% 15% 7% -2.4 31.5 -64.8 -3.0 -17.8 -57.5 -2.6
2003 886 0.00 0.38 -0.11 14% 19% 66% 14% 12% 9% 0.4 49.8 -47.7 -1.5 -5.9 -5.1 -0.2
2004 839 0.17 0.39 -0.10 18% 17% 62% 12% 13% 9% 19.6 42.7 -40.2 -2.3 -5.8 13.1 0.6
2005 934 0.16 0.36 -0.09 19% 16% 63% 19% 16% 6% 20.9 40.2 -41.0 -4.3 -23.5 -9.9 -0.4
Avg. 878 0.08 0.37 -0.11 17% 16% 65% 13% 14% 8% 9.1 40.9 -48.1 -2.8 -13.3 -15.2 -0.7
vs. MLB 0.04 0.02 -0.01 -14% -4% 21% 2% -3% -1% 2.3 -5.7 -20.5 3.7 2.9

Lowe’s line drive rate was a low 17% in 2004, so line drives didn’t cause his low out percentage. Basically, his outfield flies were caught for outs just 61% of the time. No matter how you cut it, Lowe was robbed by his fielders or the Green Monster OR he just gave up too many hard-hit balls or the balls landed in bad zones. I didn’t watch him enough to know, but I’ll bet a lot of Red Sox fans have their own opinions.

That’s a little bit of “what’s inside DER.” I simply wanted to see how much differences in pitcher DER can be explained by batted-ball types. The answer is “not a lot”—you will usually need to examine the out rates of each type of batted ball for each pitcher to get a feel for his DER.

Big Footnote

After I published the “How Much is a Batted Ball Worth” article in the Hardball Times Annual, someone pointed out to me that I could have used better run values. And when I saw someone else write in his blog that “Studes shows that a ground ball is a negative event,” I realized that he was right.

The run values I used in the article (and in the pitcher tables included in this article) are relative run values (I call them net run values), by which I mean they are relative to the average plate appearance. So the average plate appearance is worth zero runs in this context, because all the other values are expressed as a difference from the average. In other words, a ground ball is worth less than an average plate appearance, but it’s not a negative event. A team that hits all ground balls will still score a run or two.

To help clear up the confusion, let me post the following table with two sets of run values. The first is the set I published in the Annual, based on “net run values,” where the overall average is zero. The second column is based on absolute runs scored in a game, where the overall average is around 4.6. As you can see, a ground ball does have a positive value in the second column.

              Net Runs   Runs
Strikeouts      -0.29   -0.11
Walks            0.30    0.30
HBP              0.34    0.34
Infield Fly     -0.24   -0.07
Outfield Fly     0.03    0.17
Line Drive       0.36    0.40
Groundball      -0.10    0.03
Bunts           -0.10    0.04

I’m sure this is confusing, and I apologize about that. The basic difference between the two columns is the relative value given to an out. For a better understanding of what I’m talking about, you might want to read Tangotiger’s excellent article How are Runs Really Created? (Part Two).

References & Resources
Actually, Tangotiger’s three-part series on how runs are really created is one of the best and most important baseball stats articles of the last few years. If you haven’t read (or even if you have), I encourage you to read it now:
Part One
Part Two
Part Three

David Cameron has an excellent overview of all the various defensive rating systems being published and quoted these days.

Our baseball stats are compiled by Baseball Info Solutions. If you’re interested in acquiring great baseball stats, contact them.

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