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

No 20 Game Winners

An interesting and surprising fact about the 2006 season is that neither league had a single pitcher that won 20 games. Chien-Ming Wang of the Yankees and Johan Santana of the Twins both won 19 games. No one in the NL won over 16 games. Has it ever happened before that there were no 20 game winners in either league? Disregarding strike-shortened seasons, the short answer is no. However, there have been several occurrences in baseball history where one of the leagues has gone without a 20 game winner. These seasons are given in the table below (excluding strike-shortened seasons):

Year	League	Top Pitcher(s) in Wins	Top Wins
1931	NL	Elliott, Hallahan, Meine	19
1955	AL	Ford, Lemon, Sullivan	18
1960	AL	Estrada, Perry	18
1982	AL	Hoyt	19
1983	NL	Denny, John	19
1987	NL	Sutcliffe	18
2006	AL	Santana, Wang	19
2006	AL	Harang, Lowe, Penny, Smoltz, Webb, Zambrano	16

We can see from the table that not having a 20 game winner is pretty rare, and not having even a 17 game winner in the NL has never happened before. Was 2006 just an unlucky season for pitchers, or is this a manifestation of an overall decreasing trend in wins by starting pitchers? The graph below shows the highest number of wins by a pitcher in each league over the years. Not surprisingly, there has been a substantial decreasing trend, with a very slight reversal of that trend in the 1950-60 period.



The overall trend is similar in the following figure, which shows the average win totals of the top 25 wins by a pitcher in each league over the years. The increase in pitcher wins during the 1950s and 1960s is more dramatic when looking at average over 25 pitchers, as well as the corresponding return to the downward trend from the 1970s onwards.



I think we can expect a few more seasons without 20 game winners in the future. Thanks to David Gurian-Peck for his help with this analysis.