Saturday, December 30, 2006

Translation of Zone Rating into Runs Saved

In Part 1 of my 2006 fielding analysis, I ranked the Tigers on range factor and zone rating. Range factor is not so useful now that more sophisticated measures are available. Zone rating is still regarded as one of the better measures and it’s also very accessible throughout the year. Several attempts have been made to translate Zone rating into runs saved. One of the most cited methods was developed by Chris Dial who writes for Baseball Think Factory.


Dial compares each players zone rating to the average for other players at his position and then estimates the approximate run value of a ball in play at each positions. From that, he determines the runs saved a player aggregates above or below the average player at his position. In the tables below, RS= total runs saved above average and RS/150 = runs saved above average based on 150 games. The second measure allows us to better compare players with different numbers of games played.


The resulting ranks are slightly different from the zone rating ranks. This is because he does the American League separately from the National League. Zone rating, on the other hand, does not differentiate between leagues. The reason he separates the leagues is because, with pitchers batting in the National League, there are more softly hit balls and this creates somewhat of a bias.


Table 1 shows how the Tigers ranked compared to others at the same positions on RS and RS/150. According to this statistic, Placido Polanco saved 21 runs more than the league average based on 150 games played. Brandon Inge was 20 runs above league average. Those are impressive numbers. Theoretically, each is worth 2+ wins compared to the average player with their fielding over 150 games. Chris Shelton also ranked high (17 RS/150 games) topping all first basemen in baseball on this statistic. The only Tiger regular who fell below the league average was Magglio Ordonez (-2 runs per 150 games).



Table 1: Runs Saved by Tigers Fielders in 2006.


POS

Player

#

ZR

ZR Rank

RS

RS Rank

RS/150

RS/150 Rank

1B

Casey

27

.871

4

4

6

6

4

1B

Shelton

27

.913

1

12

1

17

1

2B

Polanco

29

.881

2

14

2

21

2

3B

Inge

30

.825

2

20

1

20

2

SS

Guillen

30

.832

15

2

13

3

13

LF

Monroe

28

.855

18

1

15

2

14

CF

Granderson

27

.886

10

5

10

6

9

RF

Ordonez

27

.864

17

-2

17

-2

17

Friday, December 29, 2006

Tigers Fielding Analysis for 2006

Today, I’m beginning a series of posts looking at individual fielding statistics for the Tigers and the rest of baseball in 2006. It is more difficult to measure fielding than hitting or even pitching so I will discuss several different options. I will start with the most basic of fielding stats and work my way up to the more sophisticated modern methods. Finally, I will rank the players at each position by aggregating all the stats. Today I’ll give a brief history of fielding stats and a discussion of the most frequently used measures. After that, I’ll show how the Tigers rank on these measures. In future posts, I’ll discuss some of the newer fielding measures.


The most commonly reported fielding measure is fielding percentage (FPCT) which is the infrequency with which fielders make errors on balls which they reach. It is calculated as (Total plays – errors)/total plays. Not making errors is a positive thing so this statistic has some value. It has also some important flaws though. First, errors are subjective and judgement varies from one official scorer to the next.


More importantly, FPCT says nothing about range. Some players get to a lot of balls which other players can not reach. Measurement of range is an area of sabermetrics which is still developing. The two most accessible range statistics, Range Factor (RF) and Zone Rating (ZR), are discussed below.

Range Factor (RF) was originated by Al Wright in the 1870s but it was virtually ignored for over 100 years until Bill James re-introduced it around 1980. Range Factor = (put outs + assists)/games. One of the limitations of RF is that it is a team dependent statistic. For example, an outfielder playing behind a predominantly groundball staff will have fewer opportunities than an outfielder on a staff with a lot of fly ball pitchers. Similarly, the range factors of all fielders on a team will be affected if their pitchers strike out a lot of batters.

Zone Rating (ZR) was developed by STATS, Inc in the early 1990s. They divided the baseball field into zones and assigned the zones to different fielders. Zone rating is the percentage of balls hit into a player’s zone which are turned into outs. One of the problems with zone rating is that it depends on the reliability of those collecting the data. They need to judge whether balls were actually hit into the zone and distinguish between fly balls and line drives as there is a different zone for each. Another drawback of zone rating is that it treats all balls in the zone the same way even though it may be more difficult to reach some balls within the zone than others. Since Zone Rating penalizes a player for errors by considering them to be missed opportunities, it essentially makes FPCT obsolete.


Table 1 Shows how Tiger fielders Rank on FPCT, RF and ZR. Fielding percentage does not tell us much about fielding performance but has been included on the table to show how deceptive it can be in evaluation of fielding. The discrepancies between range factor and zone rating, two statistics which are supposed to measure the same thing tell us they are not completely reliable. zone rating is considered to more reliable because it is not as team dependent.


Based on range factor and zone rating, Sean Casey (7th in RF and 4th in ZR) and Chris Shelton (3rd, 1st) both ranked quite well among 27 first basemen with 600 or more innings. Range does not work as well for first basemen as it does for other fielders because it does not address throws taken from infielders and this is obviously an important part of their jobs. Still, it is somewhat surprising that they did so well. It will be interesting to see how they do on other metrics as I get to them.


Other Tigers who ranked highly were Placido Polanco (8th, 2nd), Brandon Inge (1st, 2nd), Curtis Granderson ranked 11th on both statistics out of 27 qualifying center fielders. Carlos Guillen (17th, 15th) ranked in the middle of the pack of 30 qualifying shortstops. Craig Monroe (25th, 18th) and Magglio Ordonez (24th, 17th) ranked below average among corner outfielders.


So, as many of us observed, the Tigers apparently had strong infield and center field defense but were not as good at the corner outfield positions. These statistics don’t really pertain to catchers so they will have to be addressed at another time.


Table 1: Tigers Fielding statistics in 2006.


POS

Player

#

FPCT

FPCT Rank

RF

RF Rank

ZR

ZR Rank

1B

Casey

27

.998

1

10.01

7

.871

4

1B

Shelton

27

.994

16

10.43

3

.913

1

2B

Polanco

29

.989

7

5.25

8

.881

2

3B

Inge

30

.960

15

3.45

1

.825

2

SS

Guillen

30

.956

28

4.42

17

.832

15

LF

Monroe

28

.984

20

1.75

25

.855

18

CF

Granderson

27

.997

2

2.66

11

.886

11

RF

Ordonez

27

.974

24

1.90

24

.864

17

.

Wednesday, December 27, 2006

Run Preventing Events

Today, I’ll continue with the batted balls versus pitchers theme which I started earlier this week. An at bat can result in any of the following events:


  • Strikeout
  • Base on balls
  • Hits batsman
  • Ground ball
  • Line drive
  • Outfield fly
  • Infield fly

Three of those events are generally favorable events for pitchers:


  • Strikeout
  • Ground ball
  • Infield fly

I will call these run preventing events (RPE). Of course, a ground ball is not as easy an out as a strikeout or an infield fly and can have a negative result for a pitcher. However, inducing a lot of ground balls will help to prevent runs over the course of a season. On the other hand, it is good for pitchers to avoid, for the most part, the following events:


  • Base on balls
  • Hits batsman
  • Line drive
  • Outfield fly

So, I thought it would be interesting to calculate the run preventing event percentage (RPE%) for American League pitchers in 2006 where RPE% = (SO + GB + IFF)/BFP. Striking out batters and inducing grounders have been shown to be repeatable skills. Getting batters to hit infield flies is not stable from year to year (correlation = .10 between 2005 and 2006). However, infield flies are relatively rare compared to other batted ball types and including them does not change the RPE% substantially in most cases. Plus, I suspect (without statistical evidence) that this is a real ability for some power pitchers.


It turns out that RPE% is fairly stable with a .66 correlation between 2005 and 2006. It can also be considered a fielding independent stat because, although the end result is not independent of fielders, getting a grounder or infield fly to happen in the first place has nothing to do with fielders. It is as stable or more stable than FIP ERA but it is not weighted and thus does not explain as much about runs allowed. RPE% is just an exploratory stat for now.


There were 48 American League starters with 125 or more innings pitched in 2006. Table 1 lists the RPE% rankings for Tigers starters. Table 2 lists the top 20 pitchers in the league. We can see that Jeremy Bonderman (RPE%=.585) ranks very well (6th in the AL) as he does on most fielding independent stats. Kenny Rogers (ranking 14th with .538) and Nate Robertson (16th with .536) are also in the top third in the league. Justin Verlander (27th with ,506) is in the middle of the pack and will likely need to improve his strike out and/or ground ball rate in 2007 if he is going to keep his ERA down.


Table 1: Run Preventing Events for Tigers Starters in 2006


Rank

Name

BFP

SO

GB

IF

RPE

RPE%

6

Bonderman

903

202

306

20

528

.585

14

Rogers

849

99

340

18

457

.538

16

Robertson

881

137

312

23

472

.536

27

Verlander

776

124

244

25

393

.506

---

Ledezma

264

39

67

15

121

.458

---

Maroth

234

24

81

4

109

.466

---

Miner

398

59

144

8

211

.530


Table 2: Top 20 AL Starters by RPE% in 2006


Rank

Name

Team

BFP

SO

GB

IF

RPE

RPE%

1

Halladay

TOR

876

132

404

22

558

.637

2

Hernandez

SEA

816

176

331

10

517

.634

3

Wang

NYA

900

76

484

7

567

.630

4

Westbrook

CLE

904

109

447

7

563

.623

5

Burnett

TOR

577

118

208

14

340

.589

6

Bonderman

DET

903

202

306

20

528

.585

7

Santana

MIN

923

245

255

32

532

.576

8

Sabathia

CLE

802

172

261

26

459

.572

9

Mussina

NYA

804

172

251

36

459

.571

10

Bedard

BAL

844

171

292

14

477

.565

11

Kazmir

TB

610

163

165

14

342

.561

12

Haren

OAK

930

176

316

29

521

.560

13

Schilling

BOS

834

183

247

28

458

.549

14

Rogers

DET

849

99

340

18

457

.538

15

Escobar

LAA

789

147

263

13

423

.536

16

Robertson

DET

881

137

312

23

472

.536

17

Contreras

CHA

833

134

283

29

446

.535

18

Johnson

NYA

860

172

258

30

460

.535

19

Millwood

TEX

907

157

309

18

484

.534

20

Beckett

BOS

868

158

282

23

463

.533

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