Tuesday, January 01, 2008

Revised Zone Rating

This is the third part of my series on fielding. The Table of Contents for the series is listed below:

Basic fielding stats
Converting Zone Rating to something useful
Revised Zone Rating
Probabilistic Model of Range
Fielding Bible
Ultimate Zone Rating
Fan Fielding Survey versus range measures
Outfield arms
Ranking the second basemen
Ranking the shortstops
Ranking the third basemen
Ranking the first baseman
Ranking the center fielders
Ranking the right fielders
Ranking the left fielders
What about catchers?

After John Dewan left STATS and founded Baseball Info Solutions (BIS), he developed a new version of Zone Rating (ZR) which he called Revised Zone Rating (RZR). There are some differences between ZR and RZR. First, ZR uses data collected by STATS while RZR uses data gathered by BIS.

Another important distinction is that RZR separates balls hit outside a fielder's zone from balls inside a fielder's zone. There are a couple of reasons why it is useful to analyze balls outside the zone separately from balls hit inside the zone. Plays outside of a player's zone are typically more difficult than plays within the zone. Also, although making a large number of plays outside your zone is probably a good thing in most cases, it is possible that a player might be making some plays that a teammate could have handled just as easily. Thus, I think it can be valuable to look at the numbers of plays made inside and outside the zone before combining them.

One more difference between ZR and RZR is that RZR does not give a player extra credit for having both an assist and a putout on a double play. Being able to turn double plays is a valuable skill but a statistic that is mostly a measure of range should not credit two plays to a player that really made one. Thus, I think this is a good improvement.

The Hardball Times database includes the following statistics: Balls In Play within a fielder's zone (BIZ), Plays made in the zone (PLAYS), RZR or percentage of BIZ converted into outs, and plays made outside the zone (OOZ). Justin Inaz who writes the blog "On Baseball and the Reds" has developed an algorithm which combines RZR and OOZ and translates these numbers into plays made above average (PMAA) and runs saved above average (RSAA).

Justin first calculates the proportion of plays made per BIZ for all players combined at each position and considers that to be the expected ratio of plays made in zone (EXPPRATIO). From that, he calculates for each player, the plays made in zone above/below the MLB average (PIZ AA):

PIZ AA = PLAYS - BIZ*EXPPRATIO

He then assumes that the number of balls hit into the zone is correlated with the number of balls hit outside the zone. Considering that assumption, he calculates OOZ per BIZ for all players combined at each position (EXPORATIO). From that, he gets for each player, the plays made outside the zone above/below the MLB average (OOZ AA):

OOZ AA = OOZ - BIZ*EXPORATIO

Finally, he combines plays made inside the zone and plays made outside the zone to get PMAA:

PMAA = PIZ AA + OOZ AA

That can then be translated into Runs Saved Above Average (RSAA) the same way we did with Zone Rating. The results for the Tigers in 2007 are shown in the table below. Justin included results for all players in 2007 in a google spreadsheet.

Using Jacque Jones as an example, Table 1 is read as follows:

INN = Jones played 645 innings in centerfield
RZR = Converted 92.5% of balls hit in zone to outs
OOZ = 35 out of zone plays made
PIZ AA = Given his opportunities, he made 6 more plays in his zone than the average CF
OOZ AA = 8 more plays made out of zone than average
PMAA = 14 more total plays made than average
RSAA = 12 runs saved above average
PMAA/150 = 29 plays made per 150 games above average
RSAA/150 = 24 runs saved per 150 games above average

Table 2 compares RSAA/150 for Revised Zone Rating versus Zone Rating. The first thing to notice is that ZR appears to a bit more conservative than RZR That is, looking at all MLB players, RZR has higher highs and lower lows than ZR. The median still falls right around zero for both measures though as it should. There are some noticeable differences for individual players. First, Renteria is above average on RZR (+5) and below average on ZR (-9). Conversely, Magglio Ordonez is below average on RZ (-5) and above average on ZR (+10). Sean Casey's numbers (-8, 8) also are different for the two measures. This is why it is important to look at more than one range measure.

The way I look at it is that the very good fielders (e.g. Curtis Granderson, Jones, Brandon Inge) perform well on every measure and the poor fielders (e.g Miguel Cabrera, Carlos Guillen) perform poorly on every measure. The fielders who fall between very good and poor will go up and down according to the measure. I'm going to show you a couple of more measures. Then I will take the average of all the measures for each player and rank all the fielders in baseball by position.


Table 1: Plays Made and Runs Saved by Tigers fielders in 2007 according to RZR

POS

PLAYER

INN

RZR

OOZ

PIZ AA

OOZ AA

PMAA

RSAA

PMAA/150

RSAA/150

1B

Casey

989

.707

22

-5

-2

-8

-6

-10

-8

2B

Polanco

1209

.868

39

12

2

14

11

15

12

3B

Inge

1310

.712

63

12

4

16

12

16

13

3B

Cabrera

1311

.627

50

-17

-0

-17

-13

-17

-13

SS

Renteria

1019

.815

49

-0

5

5

4

6

5

SS

Guillen

1074

.801

36

-5

-14

-20

-15

-24

-18

LF

Monroe

806

.852

34

-1

7

6

5

11

9

CF

Granderson

1285

.921

85

12

27

39

33

40

34

CF

Jones

645

.925

35

6

8

14

12

29

24

RF

Ordonez

1221

.906

29

8

-14

-6

-5

-6

-5



Table 2: Runs Saved Per 150 Games - RZR vs ZR

PLAYER

RSAA/150 (RZR)

RSAA/150 (ZR)

Granderson

34

10

Jones

24

9

Inge

13

12

Polanco

12

4

Monroe

9

7

Renteria

5

-9

Ordonez

-5

10

Casey

-8

8

Cabrera

-13

-16

Guillen

-18

-7

2 comments:

  1. Just looking at the final result, this looks more accurate than ZR.

    One question I have is things like pop-ups. Much of the time, it could be anyone's ball but only one gets the credit.

    Nice analysis.

    ReplyDelete
  2. I'm glad you brought that up. Pop ups are not included for infielders in ZR or RZR. PMR (the next method I'll get to) does include pop ups for infielders. I'm not sure which way is the best way. You are right that sometimes it doesn't say anything about a player's range. However, there are some players like Inge who seem to catch pop ups that others can't reach. It's tricky.

    Lee

    ReplyDelete

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