Tigers Bullpen Doing Fine So Far

In a recent post, I used the RE24 statistic to measure batting contribution including situational hitting.  The statistic is appealing because it gives batters more credit for hits with runners on base than for hits with the bases empty.  This concept can also be applied to pitchers, relievers in particular.

Statistical evaluation of relievers is difficult for a couple of reasons:

1. They pitch so few innings that their statistics can be influenced heavily by a couple of really bad outings.
2. Their actual value depends on game situations more than any other player (this problem will be addressed here)

Using ERA to evaluate relievers is problematic because relievers often make appearances with runners on base and give up other pitcher's runs. So, a pitcher could have a low ERA without actually being that effective. FIP which is based on walks, strikeouts and home runs allowed rather than runs allowed is better but it still does not consider the game environments in which a reliever pitched.

The RE24 metric estimates the number of runs a pitcher saved or cost his team based on his numbers of singles, doubles and all other events allowed including outs.  It also considers the situations in which these events happened.  For example, if Tigers southpaw Tom Gorzellany enters a game with two men on base and nobody out and retires the side he will get more credit than if he comes in with the bases empty.  Gorzellany gets more points in the first scenario because there was greater potential for run scoring.  Thus, Gorzellany saves the Tigers more runs if he frequently pitches well with runners on base than if he always starts an appearance with the bases empty.

The RE24 for all American League teams is shown in Table 1 below.  The Tigers have an RE24 of -17.9 which says that their bullpen has saved them an estimated 18 runs compared to an average staff with the same number of outs. The interpretation is a little misleading because the average also includes starters.  However, all bullpens are compared to that same average, so the ranks are telling and only the Royals (35.9) and Astros (23.6) have been better than the Tigers.  

Table 1: AL Team RE24, May 24, 2015

Team	RE24
Royals	35.9
Astros	23.6
Tigers	17.9
Rays	7.3
White Sox	4.2
Angels	3.0
Twins	3.0
Blue Jays	-0.5
Yankees	-1.0
Red Sox	-1.1
Orioles	-4.0
Indians	-7.7
Rangers	-8.6
Mariners	-11.6
Athletics	-22.5

Data source: FanGraphs.com

The American League RE24 leaders among relievers are shown in Table 2 below.  Astros right hander Will Harris heads the list at 11.1 followed by Roberto Osuna of the Blue Jays (9.9).  The Tigers have two pitchers in the top 15 - closer Joakim Soria (6.8) and middle man Alex Wilson (6.0).

Table 2: AL RE24 Leaders, May 24, 2015

Name	Team	RE24
Will Harris	Astros	11.1
Roberto Osuna	Blue Jays	9.9
Wade Davis	Royals	8.8
Dellin Betances	Yankees	7.4
Brandon Gomes	Rays	6.9
Joakim Soria	Tigers	6.8
Glen Perkins	Twins	6.6
Andrew Miller	Yankees	6.3
David Robertson	White Sox	6.2
Alex Wilson	Tigers	6.0
A.J. Ramos	Marlins	6.0
Shawn Tolleson	Rangers	5.9
Brad Boxberger	Rays	5.8
Zach Duke	White Sox	5.7

Data source: FanGraphs.com

Table 3 shows the performance rest of the Tigers in terms of RE24 including Gorzellany (3.5) and left hander Blaine Hardy (2.4).   The only current Tigers relievers below zero are Joba Chamberlain (-0.2) and Al Alburquerque (-0.7) and they are no where near the bottom of the league.

Table3: Tigers RE24, May 24, 2015

Player	RE24
Joakim Soria	6.8
Alex Wilson	6.0
Tom Gorzelanny	3.5
Blaine Hardy	2.4
Angel Nesbitt	0.7
Joba Chamberlain	-0.2
Al Alburquerque	-0.7

Data source: FanGraphs.com

Can the Tigers bullpen keep up their surprising third place ranking?  Without much dominant stuff on the staff, it will not be easy.  Their 3.65 FIP is good enough for 5th in the league, but their strikeout rate of 6.9 per nine innings is second worst only to the Twins.  The fact that the starting staff leads the league with 6.2 innings per start has helped limit the exposure of what was supposed to be a leaky pen.  With Anibal Sanchez struggling and Kyle Lobstein now on the disabled list with a sore shoulder, it is questionable how long that will last.

Still, it's hard not to be happy with the bullpen performance so far.  This was a group which many predicted would be close to the bottom of the league.  They will likely need re-enforcements soon and  hopefully rehabbing flame thrower Bruce Rondon will be one of them.  They might not need as much help as originally thought though.