Did Lefty Grove Lead the AL in Championship Win Probability Added (cWPA) in 1931 as Both a Starter and a Reliever?

What is cWPA? See Single-Season Leaders & Records for Championship WPA (cWPA) from Baseball Reference:

"Given average teams, this is the change in probability, displayed in percentage points. A change of +/- 100% would indicate one world series win added or lost."

If a pitcher or batter does well in close games late in the season, they will probably have a high cWPA. It also helps to do well late in games and be on a contender. 

Click here to see the leaders in cWPA in the 1931 AL. You will have to click on the cWPA column heading to get the pitchers ranked accordingly.

I looked at the top 16, which includes every guy with 1.0 or higher. Then I went to the Baseball Reference game logs for each guy and determined how much cWPA they had has as a starter and then as a reliever. cWPA is listed for each game and games as starters and relievers can easily be separated.

The first table shows those 16 pitchers ranked by cWPA as starters.

Player	Starter	Reliever
Lefty Grove*	16.4	4.1
Rube Walberg*	8.5	-1.3
George Earnshaw	4.1	0.8
Firpo Marberry	3.9	2.3
Roy Mahaffey	3.2	0.9
Waite Hoyt	2.1	-0.2
Herb Pennock*	1.9	0
Clint Brown	1.7	-0.2
Earl Whitehill*	1.6	0
Pat Caraway*	1.3	0
Lefty Stewart*	1.2	0
Bump Hadley	1.1	0.5
Bobby Burke*	1.0	2.0
Lefty Gomez*	0.9	2.9
Carl Fischer*	0.3	2.4
Wilcy Moore	-0.8	3.1

This does not mean that these were the top 16 in cWPA if we only counted starts, but how the top 16 overall would rank amongst themselves if we only looked at starts. Grove is the clear leader. 

Now if they are ranked by relief appearances.

Player	Starter	Reliever
Lefty Grove*	16.4	4.1
Wilcy Moore	-0.8	3.1
Lefty Gomez*	0.9	2.9
Carl Fischer*	0.3	2.4
Firpo Marberry	3.9	2.3
Bobby Burke*	1.0	2.0
Roy Mahaffey	3.2	0.9
George Earnshaw	4.1	0.8
Bump Hadley	1.1	0.5
Herb Pennock*	1.9	0
Earl Whitehill*	1.6	0
Lefty Stewart*	1.2	0
Pat Caraway*	1.3	0
Waite Hoyt	2.1	-0.2
Clint Brown	1.7	-0.2
Rube Walberg*	8.5	-1.3

 

I don't think it is likely that any other pitcher could have beaten Grove in either category. Any pitcher with less than 1.0 cWPA overall would need to have a very large negative in one of the roles. For example, to beat Grove's 4.1 in relief he would need to have had -3.3 as a starter (no one in the league was worse than 2.9 overall). So if he had 4.2 as a reliever and -3.3 as a starter, he would be 0.9 overall (and 0.9 was the next highest overall after the top 16 that I looked at here).

 

There might be some pitchers in other years who led in both roles. In Grove's time, regular starters pitched fairly often in relief.  See my post Starting Pitchers As Relievers Over Time.

 

Grove had a 31-4 record with a 2.04 ERA and 5 saves. Here are his stats in both roles:

 

Split	W	L	ERA	G	IP	OPS
as Starter	27	3	1.94	30	260.1	0.574
as Reliever	4	1	3.18	11	28.1	0.644

 

To put these numbers in perspective, the league ERA was 4.38 while the league OPS was .740.  Grove, of course, was also helped by being on a first place team