More or less about grounders

I was wondering about the biggest swings in groundball rate by hitters and pitchers from 2008 and 2009. The results were enough of a surprise to me, and enough of a lack of surprise, I figured I’d share what started as a mild curiosity.

Ground balls per plate appearance

This isn’t about the ball in play rates I typically look at, but the number of plate appearances that ended with a ground ball. This will capture pitchers who strike out fewer batters while getting the same rate of ground balls. Looking at the extremes, I found the three pitchers who made the biggest move toward more grounders and the three batters who cut down on them the most. As a general fan of pitching and a fan of the Chicago Cubs, four of the six names came as no surprise.

For both groups, a minimum of 300 plate appearances in 2009 and 500 in 2008 are required. Relative difference is included, although absolute difference was the qualifying factor.

Pitchers with most ground balls added per 100 plate appearances

Batters with most ground balls reduced per 100 plate appearances

How’s that working out for you guys?

Bottom line is results, or words to the effect. Here are some basic stats on the six subjects.

Joel Pineiro

Brian Bannister

Glen Perkins

Outside of an improved home run rate, Perkins is not like the others. He’s also a recent addition to the 15-day disabled list.

Chris Young

Derrek Lee

Ryan Theriot

Once again, we have two improved and one not so much. This time, it’s Arizona’s Chris Young, who was demoted just a couple days before Minnesota disabled Perkins.

For Lee and Theriot, the drop in double plays and pick-up in home runs stand out. Pineiro and Bannister are having far better seasons than most expected. But for Young and Perkins, there doesn’t look to be much of an upside.

I found a couple things about Perkins lurking in his PITCHf/x data.
{exp:list_maker}After throwing a mix of curves and sliders in 2008, he has abandoned the curveball in 2009.
Most of the increase in grounders comes from the fastball, where balls in play have resulted in grounders 49 percent of the time compared to 38 percent last season.
Hitters are swinging at more of his sliders, drastically reducing his called strike rate, but also yielding more whiffs and fewer line drives
Perkins’ fastball velocity ticked down each year since 2007 (92.1, 91.5, 90.4)
{/exp:list_maker}
If I hadn’t looked at Perkins’ line first, I wouldn’t have guessed he’d be doing so much worse in 2009. This doesn’t even attempt to look where or when his injury impacted his performance, and it is a small sample—hard to draw conclusions even if something looks “clear.”

Young is less confusing. He’s replaced his grounders with pop-ups. His rate of pop-ups on balls in play has doubled (to 24 percent). Meanwhile, his home runs per ball in air (pops, lines and flies) has gone from nearly 15 percent in 2007 to less than eight percent in 2008 down to four percent for 2009. There was no change in batted ball type between 2007 and 2008 to explain the drop in power, and the 2009 pop-ups aren’t enough to explain the continued drop in home runs.

Sometimes an “improved” ground ball rate isn’t a good thing. It just isn’t that simple, I say to my straw man.

References & Resources
Pitch, and some batted ball, data from MLBAM, pitch classifications by the author