Wednesday, July 13, 2011

Re-WERCing Things

Linear Weights guru Tom Tango likes to use wOBA against for pitchers as well as hitters.  However, he told me yesterday that Base Runs is preferable to trying to convert wOBA to runs as I did in my last post.  So, I'm going to do some leader boards according to Base Runs today.  It turns out they aren't radically different from the linear weights leaders presented my previous post, although linear weights seemed to inflate the value of star pitchers (runs saved above average) a little bit

The Base Runs measure was created by David Smythe in the early 1990s.  It is based on the idea that we can estimate team runs scored if we know the number of base runners, total bases, home runs and the typical score rate (the score rate is the percentage of base runners that score on average.  Base Runs also works well for individual pitchers.  The complete formula can be found here.

Justin Verlander has 39 Base Runs Against in 151 innings so far this year.  This means that he should have allowed an estimated 39 runs based on the number of base runners, total bases and home runs he has allowed.  He has allowed 39 actual runs, so runs are scoring against him at the exact rate you would expect.

Verlander has allowed 33 Base Runs Above Average (RAA) which means that he has saved the Tigers an estimated 33 runs compared to the average pitcher in the same number of innings.  Table 1 shows that he is tied for first in the American League with Angels ace Jered Weaver.


Table 1 - AL Base Runs Allowed Above Average Leaders as of July 10

Player
Team
IP
Base Runs
Against
RAA
Jered Weaver
LAA
140.1
33
33
Justin Verlander
DET
151.0
39
33
Josh Beckett
BOS
111.0
27
25
James Shields
TBR
142.2
44
24
Dan Haren
LAA
134.1
40
24
CC Sabathia*
NYY
145.2
47
22
Felix Hernandez
SEA
144.0
49
19
Michael Pineda
SEA
113.0
35
18
Philip Humber
CHW
107.1
34
17
Alexi Ogando
TEX
104.2
33
16


Table 2 shows that Verlander has allowed 2.32 Base Runs per nine innings.  About 93% of runs are earned, so multiply this result by .93. to put it on the same scale as ERA. The final result is a weighted component ERA.  Although, I am no longer using linear weights here, I'll keep calling it WERC because others have said the like the name. It's really not a novel idea though.  U.S. Patriot of Walk Like a Saber has been using Base Runs to evaluate pitchers for a while but prefers to not convert to the ERA scale.

Getting back to the example, Verlander has a 2.16 WERC.  Since his Base Runs Allowed is the same as his actual runs allowed, this is almost the same as his real ERA.  He is third in the league behind Weaver (1.98) and Josh Beckett of the Red Sox (2.06). 


Table 2: AL WERC Leaders as of July 10


Player
Team
IP
Base Runs/9 IP
WERC
Jered Weaver
LAA
140.1
2.13
1.98
Josh Beckett
BOS
111.0
2.21
2.06
Justin Verlander
DET
151.0
2.32
2.16
Dan Haren
LAA
134.1
2.68
2.49
James Shields
TBR
142.2
2.77
2.58
Michael Pineda
SEA
113.0
2.83
2.63
Philip Humber
CHW
107.1
2.87
2.67
Alexi Ogando
TEX
104.2
2.89
2.68
CC Sabathia*
NYY
145.2
2.92
2.72
Felix Hernandez
SEA
144.0
3.09
2.87

The raw data used to create the statistics in this post was extracted from Baseball-Reference.

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