Giving Pitchers Credit for Infield Flies with EO%

Much has been written about fielding independent events - strikeouts, walks, hit batsmen and homeruns - over the last several years.  Those are things which a pitcher controls with minimal contribution from fielders.  No event is totally independent of teammates of course.  For example, an outfielder can reach over the fence to prevent a home run.  Additionally, recent research on framing pitches suggest that catchers can have some influence over strikeouts and walks.  Still, pitchers do control these events for the most part.

Another event which is mostly responsibility of the pitcher, and could be considered fielding independent, is the infield fly.  While there are certainly fielders involved in getting outs on infield flies, there is not a lot of difference among major league infielders in their ability to catch infield flies.  Regardless of the pitcher or the team, when you see a pop up in the infield it almost always leads to an out.  Table 1 below shows that batters hit .023 and slugged .027 on pop ups in 2012.   These rates are much lower than those for any other batted ball type including ground balls.

Table 1: Batting Statistics by Batted Ball Type, 2012

Batted Ball Type	BA	SLG	OPS
Ground ball	.241	.260	.501
Infield fly	.023	.027	.050
Outfield fly	.273	.741	1.014
Line drive	.722	.975	1.697

 Data source: Retrosheet.org

The notion that infield flies are essentially fielding independent events is not not a new one.  Dave Cameron and Tom Tango have both suggested adding infield flies to the Fielding Independent Pitching (FIP) statistic similar to how strikeouts are already included.  It's true that infield fly ball rate is less predictive of future performance than strikeout rate, but predicting the future is not the only function of FIP.  It is also used to evaluate past performance.

Since infield flies lead to outs almost as frequently as strikeouts, I have combined the two into a statistic I call Easy Out Percentage - EO%   It is simply strikeouts plus infield flies divided by batters faced.  As mentioned above, this could also be incorporated into FIP, but I'll keep it simple for now.  Table 2 below shows that Tigers right hander Max Scherzer led the majors with a 36.0 EO% in 2012.  Teammate Justin Verlander was third at 35.5%.  The National League leader was Stephen Strasburg of the Nationals (35.8%).   

Table 2: Easy Out Percentage (Strikeouts and Infield Flies), 2012

Pitcher	Team	BFP	K	IFFB	EO%
Max Scherzer	Tigers	787	231	52	36.0
Stephen Strasburg	Nationals	653	197	37	35.8
Justin Verlander	Tigers	956	239	100	35.5
Yu Darvish	Rangers	816	221	61	34.6
Clayton Kershaw	Dodgers	901	229	74	33.6
R.A. Dickey	Mets	927	230	81	33.5
Chris Sale	White Sox	772	192	64	33.2
Cole Hamels	Phillies	867	216	71	33.1
Cliff Lee	Phillies	847	207	72	32.9
Matt Moore	Rays	759	175	71	32.4
Phil Hughes	Yankees	815	165	93	31.7
Felix Hernandez	Mariners	939	223	67	30.9
CC Sabathia	Yankees	833	197	60	30.9
David Price	Rays	836	205	52	30.7
Gio Gonzalez	Nationals	822	207	45	30.7
Bruce Chen	Royals	827	140	111	30.4
Jake Peavy	White Sox	882	194	70	29.9
J.A. Happ	- - -	627	144	43	29.8
Lance Lynn	Cardinals	744	180	41	29.7
Matt Cain	Giants	876	193	67	29.7

Data source: FanGraphs.com 

The majority of pitchers rank similarly on K% and EO%, but there are some exceptions.  One such outlier was Bruce Chen of the Royals who ranked 73 out of 103 pitchers (with 600+ batters faced) in strikeout percentage, but 16th in EO%.  Another was Tigers right hander Rick Porcello - 95th in K% and 52nd in EO%.  The reason for the disparity was that Chen (17.6%) and Porcello (15.8%) ranked one and two in infield flies per batted ball even though they didn't whiff a lot of batters,

It is important to keep in mind that the ability to to induce popups has not been shown to be a highly repeatable skill for most pitchers.  For example, Porcello's rate in 2012 was by far the highest in his career.  In his four years, he gas posted rates of 4.9%, 7.7%, 10.5% and 15.8%. The increasing trend may or may not be a fluke, but the huge jump in 2012 in particular probably was.  Regardless, his infield flies in 2012 added value and he should get credit for it.