October 19, 2009

Ahead in the Count

Park-Adjusted Slugging

by Matt Swartz

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A few weeks ago, I introduced a new metric to evaluate team defense called Slugging on Balls in Play (SLGBIP), to be used in conjunction with Defensive Efficiency (DE) or Park-Adjusted Defensive Efficiency (PADE). The importance of this stat is that a simple consideration of how many outs a team makes does not entirely evaluate how well the team prevents runs. When we evaluate team offense, we consider team slugging more important than team batting average; if a team defense's only goal was to make outs, they would play their outfielders in and their corner infielders off the lines constantly. Since they do not, seeing how well they prevent extra-base hits is important as well.

However, many readers pointed out that certain parks are more conducive to preventing extra-base hits than others, and a metric such as Slugging on Balls in Play might have some inherent biases towards teams who play in stadiums where it is difficult to hit doubles and triples. Fortunately, there was already a method in place to adjust for this. In 2003, James Click introduced a new measure, PADE, in which he made park factors equal to the ratios of Defensive Efficiency at home versus on the road for the previous three years. I decided to reevaluate my analysis of 2007-2009 from my previous article by generating ratios of home and road Slugging on Balls in Play for 2007-2009. I did this for all teams except for the three that moved into new stadiums in the last three years: the Nationals, Yankees, and Mets. For the Yankees and Mets, I just used 2009 data to create their SLGBIP Park Factor for their current home fields, and 2006-2008 data to create their SLGBIP Park Factor for their previous home fields. For the Nationals, I used 2005-2007 to get their RFK Park Factor, and 2008-2009 to get their Nationals Park PF. Then I generated Park-Adjusted Slugging on Balls in Play (for yet another acronym, how about PASBP), which is transformed to represent the percentage difference in SLGBIP that their defense allowed relative to league average, and took the negative of this value so that positive numbers imply good defense. Here are the 2009 SLGBIP and PASBP rankings next to each other:

2009
Rank Team     SLGBIP  Rank Team       PASBP
  1  Mariners  .354     1  Mariners   7.293
  2  Dodgers   .360     2  Giants     7.156
  3  Reds      .371     3  Cubs       5.927
  4  Giants    .371     4  Dodgers    3.990
  5  Cubs      .372     5  Reds       3.352
  6  Rangers   .374     6  Rangers    3.318
  7  Cardinals .379     7  Tigers     1.334
  8  Yankees   .379     8  Rockies    0.724
  9  Padres    .380     9  Marlins    0.432
 10  Phillies  .381    10  Red Sox    0.425
 11  Rays      .383    11  Rays       0.276
 12  Tigers    .383    12  Phillies   0.130
 13  Twins     .386    13  Indians    0.130
 14  Angels    .391    14  White Sox -0.419
 15  White Sox .392    15  Cardinals -0.682
 16  Athletics .394    16  D'backs   -0.938
 17  Mets      .395    17  Royals    -1.185
 18  D'backs   .397    18  Twins     -1.150
 19  Rockies   .397    19  Angels    -1.680
 20  Brewers   .397    20  Yankees   -2.737
 21  Indians   .400    21  Padres    -4.081
 22  Marlins   .402    22  Orioles   -4.428
 23  Astros    .406    23  Blue Jays -4.997
 24  Pirates   .406    24  Braves    -5.739
 25  Red Sox   .406    25  Brewers   -5.791
 26  Braves    .406    26  Mets      -5.882
 27  Blue Jays .406    27  Athletics -7.120
 28  Royals    .406    28  Astros    -7.731
 29  Orioles   .410    29  Pirates   -9.193
 30  Nationals .418    30  Nationals -9.420

The most obvious example of a big change between the two rankings is the Red Sox, who went from 25^th in SLGBIP to 10^th in PASBP. That makes good sense, because the Green Monster is very conducive to doubles, and ignoring that makes it look like the Red Sox defense is especially vulnerable to surrendering doubles. The Padres went in the other direction, sitting at a respectable ninth in SLGBIP, but after adjusting for park, they fell to 21^st. Their SLGBIP at home over the last three years is .357, but on the road it is .409; Petco Park is very difficult to hit extra-base hits in, as well as being difficult to hit home runs. Other notable changes included the Marlins, who went from 22^nd to ninth after adjusting for park, the A's going from 16^th down to 27^th, and the Yankees falling from eighth to 20^th, while the Royals went from 28^th to 17^th, and the Rockies saw an improvement from 19^th to eighth after adjusting for the fact that they play in double-icious Coors Field.

How does this effect the evaluation of previous years? Let's look at 2008 and 2007:

2008
Rank Team     SLGBIP  Rank Team        PASBP
  1  Rays      .376     1  Red Sox     7.531
  2  Brewers   .378     2  Cubs        4.599
  3  Mets      .379     3  Marlins     4.310
  4  Blue Jays .380     4  Indians     3.564
  5  Padres    .382     5  Rays        2.873
  6  Red Sox   .382     6  Royals      2.521
  7  Athletics .384     7  Brewers     2.240
  8  Orioles   .386     8  Blue Jays   2.126
  9  Cubs      .386     9  Orioles     2.106
 10  Angels    .386    10  Angels      0.664
 11  Dodgers   .389    11  Mets        0.501
 12  Phillies  .390    12  Phillies    0.461
 13  Indians   .390    13  D'backs    -0.129
 14  Marlins   .391    14  Giants     -0.302
 15  Twins     .392    15  Dodgers    -1.014
 16  Astros    .394    16  Astros     -1.017
 17  Royals    .395    17  Athletics  -2.040
 18  Nationals .397    18  Twins      -2.161
 19  Yankees   .399    19  Padres     -2.824
 20  Cardinals .400    20  White Sox  -2.825
 21  D'backs   .401    21  Tigers     -3.653
 22  White Sox .403    22  Nationals  -3.682
 23  Tigers    .406    23  Cardinals  -3.733
 24  Giants    .407    24  Yankees    -3.764
 25  Braves    .408    25  Rockies    -3.834
 26  Mariners  .409    26  Braves     -3.984
 27  Rockies   .422    27  Mariners   -5.908
 28  Pirates   .423    28  Rangers    -6.856
 29  Reds      .423    29  Reds       -9.090
 30  Rangers   .424    30  Pirates   -10.697

2007
Rank Team     SLGBIP  Rank Team        PASBP
  1  Blue Jays .364     1  Red Sox     9.333
  2  Red Sox   .378     2  Blue Jays   7.201
  3  Padres    .379     3  Cubs        6.541
  4  Cubs      .382     4  Rockies     4.333
  5  Nationals .384     5  Indians     3.480
  6  Mets      .388     6  Braves      1.946
  7  Braves    .388     7  Orioles     1.635
  8  Orioles   .392     8  Giants      1.601
  9  Rockies   .393     9  D'backs     1.405
 10  Cardinals .394    10  Nationals   0.851
 11  Indians   .394    11  Tigers     -0.129
 12  Athletics .395    12  Rangers    -0.408
 13  Tigers    .396    13  Mets       -0.850
 14  Dodgers   .397    14  Cardinals  -1.081
 15  Yankees   .397    15  Padres     -1.247
 16  Twins     .398    16  Royals     -1.983
 17  D'backs   .398    17  Dodgers    -2.104
 18  Rangers   .402    18  White Sox  -2.115
 19  Giants    .403    19  Yankees    -2.230
 20  White Sox .404    20  Twins      -2.658
 21  Angels    .405    21  Phillies   -2.947
 22  Astros    .407    22  Marlins    -3.035
 23  Phillies  .407    23  Angels     -3.063
 24  Brewers   .415    24  Astros     -3.504
 25  Royals    .418    25  Athletics  -3.850
 26  Pirates   .418    26  Brewers    -6.378
 27  Reds      .418    27  Reds       -6.753
 28  Mariners  .420    28  Mariners   -7.655
 29  Marlins   .426    29  Pirates    -8.666
 30  Rays      .441    30  Rays      -12.908

The biggest changes in evaluation of team defense's SLGBIP prevention in 2008 were the Padres' dropping from fifth way down to 19^th, with the Royals jumping up from 17^th to sixth, and the Marlins moving from 14^th all the way up to an impressive third place in PASBP. The biggest differences in 2007 were that the A's fell from 13^th to 25^th and the Padres fell from third to 15^th, while the Giants climbed up from 19^th up to eighth.

Comparing 2008 to 2009, we see several teams whose PASBP changed significantly. The Mariners went from 27^th to first in SLGBIP in just one season. The Reds jumped from 29^th all the way up to fifth, the Rangers from 28^th to sixth, and the Rockies went from 25^th to eighth. The Brewers plummeted from eighth down to 25^th, the Mets tanked from 11^th to 26^th, and the Orioles went from ninth to 22^nd. There were some real changes in PASBP in this past year, as four of the bottom six teams from 2008 found their way into the top ten teams of 2009.

The transition from 2007 to 2008 saw fewer changes, but the Rays did rise from dead last in 2007 to fifth in 2008, while Colorado fell from fourth to 25^th. The Braves also fell, from sixth to 26^th, but the Brewers rose from 26^th to seventh and the Marlins went from 22^nd to third. Many of those teams did regress back in 2009, but the Rays did manage to have an 11^th-ranked PASBP after their huge jump from 2007 to 2008, and the Marlins stayed up at ninth in 2009. The Rockies went back up to eighth after their decline, while the Braves stayed down, only ranking 24^th in 2009. The Brewers' ascension was nearly completely reversed, going all the way back down to 25^th.

It appears that including this type of information is important. Although Slugging on Balls in Play is a useful statistic to evaluate team defense, it is probably more susceptible to park effects. Doing this kind of adjustment appears to have focused the analysis and improved the evaluation of team defense. Even after accounting for team defense in 2009, it is clear that the Mariners and Giants both played extraordinary team defense this year, especially in the outfield. As both clubs were not strong in team defense in 2008, this raises a lot of questions, especially in light of the sudden lack of persistence in team defensive rankings. Recall that last week I explained that Defensive Efficiency in 2009 had a negative correlation with 2008, the first time this has happened in the Retrosheet era. In fact, this lack of persistence appears to be consistent with respect to slugging as well: the correlation between 2007 and 2008 PASBP was .41, but the correlation between 2008 and 2009 was positive, but only .09. It is certainly notable that, defensively, baseball is changing rapidly as more information becomes available. Looking at all of these metrics throughout the 2010 season will be interesting and enlightening as we try to figure out what is happening in the game.

Matt Swartz is an author of Baseball Prospectus. 
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