What Happens to Ground Balls Hit Off Tigers Pitchers?

As often happens in a Rick Porcello start, a discussion about Tigers infield defense broke out on Twitter yesterday afternoon.  The Tigers defense was not terrible behind Porcello Saturday, but there were a couple of seeing-eye singles, which may or may not have been converted into outs by better infielders.  The theory is that, because Porcello does not strike out many batters out and induces a lot of ground balls, he would benefit more from a team with a better infield defense than the Tigers.

I decided to look into this issue further using the retrosheet databases.  The 2013 data are not yet available, but I was able to look at what happened on ground balls from 2010-2012.  Table 1 below shows that there were 5,913 ground balls off the Tigers staff during that period.  Of those, 1,523 resulted in hits yielding a batting average of .258.  That was the highest batting average in the majors which probably doesn't surprise anyone that has watched the Tigers defenders stagger around the infield in recent years.

The MLB batting average on ground balls was .241, so the Tigers were .017 higher than average.  There are about 2,000 ground balls per year, so that is 34 more hits per year on ground balls more than average.  The average failure to convert a batted ball into an out is 0.75 runs, so that comes out to about 25 runs per season, which is significant.

The lowest batting average on ground balls was .221 achieved by the Blue Jays.  In comparison to Toronto, the Tigers allowed 74 extra hits on ground balls per year which translates into about 55 runs.  That illustrates the value of a superior infield defense.

Table 1: Batting Average on Ground Balls Versus Pitchers, 2010-2012

Team	GB	H	BAA
TOR	6,104	1,349	.221
WAS	5,975	1,330	.223
ANA	5,934	1,334	.225
OAK	5,894	1,346	.228
TBA	5,629	1,299	.231
BOS	5,892	1,364	.232
LAN	5,640	1,306	.232
SEA	5,908	1,372	.232
SDN	5,938	1,384	.233
ATL	6,155	1,440	.234
TEX	5,619	1,317	.234
SLN	6,602	1,565	.237
SFN	5,717	1,356	.237
PHI	5,905	1,413	.239
COL	6,182	1,483	.240
CLE	6,525	1,566	.240
CIN	5,977	1,437	.240
NYN	6,010	1,464	.244
ARI	5,857	1,433	.245
PIT	6,275	1,541	.246
MIL	5,698	1,411	.248
BAL	6,112	1,515	.248
CHN	5,714	1,422	.249
HOU	6,060	1,540	.254
NYA	5,861	1,490	.254
MIA	5,976	1,527	.256
KCA	5,978	1,529	.256
CHA	5,910	1,518	.257
MIN	6,416	1,649	.257
DET	5,913	1,523	.258

 The information used here was obtained free of charge from and is copyrighted by Retrosheet.

I next looked at individual Tigers pitchers to see who might have been affected most by the porous infield defense.  Porcello's BAA on 962 ground balls was .262.  That translates into about seven hits per year, so the direct effect is not huge - an additional 0.25 to his ERA.  However, these data do not account for the effect of extra pitches thrown in order to get more outs.  Given that Porcello typically tires after about 75 pitches, this could be a problem.  It's also possible that a lack of confidence in his in infield could negatively affect pitch selection.

Interestingly, the pitcher that seems to have been affected the most by extra hits on ground balls was Max Scherzer who had a .291 BAA on ground balls.  Luckily, Scherzer does not rely nearly as much on ground balls as Porcello, but it still amounts to an estimated 8 more runs or 0.40 in ERA per year compared to the average pitcher.  This may explain why his ERA was higher than his FIP the last couple of years.

On the other hand, Doug Fister (in games with the Tigers only) and Justin Verlander each had a .212 BAA on ground balls which was considerably lower than average.  This may have been random luck or it could be that they induced weaker contact on grounders than other pitchers.  Unfortunately, data such as speed of batted balls is not yet available to the public.

Most of the Tigers pitchers did have higher BAAs than average though.  Joaquin Benoit, Phil Coke, Anibal Sanchez and Drew Smyly were all between .250-.265.  So, it does appear that in general that Tigers were adversely affected by infield defense.  I'll get back to this after the season when 2013 data are available.