Fielding Adjusted Pitcher ERAs

In a previous blog entry, we discussed team-level measures of SAFE, our Spatial Aggregate Fielding Analysis measures. One way in which these measures can be used is to re-evaluate the past performance of pitchers and account for the defense working behind them. We take the runs saved/cost by each team's defense in a given year and partition those extra runs among the pitchers based on their number of innings pitched. We then recalculate each pitchers ERAs with these extra runs saved or cost factored in. The full set of results for the 2002-2005 seasons are available for download at:


Pitcher ERA Adjustments

As a preview of the results, we give a table of the top ten relief pitchers in terms of the percentage change between their old and new (adjusted) ERAs.

PLAYER	TEAM	YEAR	IP	New ERA	Old ERA	Diff	%Diff
Dan Plesac	Phi	2003	33.1	2.19	2.7	-0.51	-19.0
Mariano Rivera	NYY	2005	78.1	1.14	1.38	-0.24	-17.4
Josh Hancock	Cin	2005	14	1.63	1.93	-0.30	-15.7
Derrick Turnbow	Ana	2003	15.1	0.68	0.59	0.09	14.6
Mariano Rivera	NYY	2004	78.2	1.67	1.94	-0.27	-14.1
Fernando Cabrera	Cle	2005	30.2	1.67	1.47	0.20	13.3
Tom Gordon	NYY	2004	89.2	1.94	2.21	-0.27	-12.0
Brian Shackelford	Cin	2005	29.2	2.15	2.43	-0.28	-11.7
Jorge DePaula	NYY	2003	11.1	0.70	0.79	-0.09	-11.5
Matt Miller	Cle	2005	29.2	2.02	1.82	0.20	11.1

We see that most pitchers which show improvement in their ERA played for the Yankees or Reds, the two teams with the worst defense in the 2002-2005 seasons. This same trend is seen in the top ten starting pitchers in terms of the percentage change between their old and new (adjusted) ERAs.

PLAYER	YEAR	TEAM	IP	New ERA	Old ERA	Diff	%Diff
Aaron Harang	2005	Cin	211.2	3.51	3.83	-0.32	-8.5
Brandon Claussen	2005	Cin	166.2	3.88	4.21	-0.33	-7.9
Jason Schmidt	2004	SF	225	2.95	3.20	-0.25	-7.8
Shawn Chacon	2005	NYY	151.2	3.19	3.44	-0.25	-7.4
Kevin Brown	2004	NYY	132	3.79	4.09	-0.30	-7.3
Jason Schmidt	2003	SF	207.2	2.17	2.34	-0.17	-7.1
Jon Lieber	2004	NYY	176.2	4.04	4.33	-0.29	-6.8
Brett Tomko	2004	SF	194.0	3.77	4.04	-0.27	-6.6
Randy Johnson	2005	NYY	225.2	3.54	3.79	-0.25	-6.5
Ramon Ortiz	2005	Cin	171.1	5.02	5.36	-0.34	-6.4