Real Groundball Rates

by
April 9, 2010

In his first start with the Angels last night, Joel Pineiro showed that the sinker he learned from Dave Duncan traveled with him to Anaheim, getting 15 groundballs in 6 innings of work. While he gave up three runs, he’ll pitch well for the Angels as long as that two-seam fastball is still diving, and there’s no indication that he lost it in the transition back to the AL.

However, this post isn’t really about Joel Pineiro. It’s about GB/FB ratio. Pineiro’s 15.00 GB/FB ratio tied with Felix Hernandez for the best of any pitcher to throw so far. However, if you sort by GB%, rather than GB/FB, you will notice that Ryan Dempster actually posted a higher groundball rate than Pineiro. Dempster ran a 75 percent GB% in his first start, compared to 71 percent for Pineiro, though his GB/FB ratio is a more pedestrian 4.50.

The difference, of course, is line drives. Dempster only gave up one, while Pineiro gave up five, and those don’t go in the GB/FB calculation. If the Twins had hit Pineiro less effectively, and those line drives had been converted into fly balls, his GB/FB ratio would have gone down, even though he would have pitched better and likely allowed fewer runs.

In other words, in this case, a higher GB/FB ratio is actually a bad thing.

Now, over a full season, this mostly evens out, and the correlation between GB% and GB/FB is pretty darn high. However, given that we have GB%, FB%, and LD%, I’d like to see GB/FB go by the wayside. It doesn’t serve any purpose, really. Why evaluate a pitcher on just two of the three batted ball types, rewarding him for giving up more of the most harmful kind?

GB% gives you all of the good information of GB/FB without any of the bad assumptions about line drive rates being equal. When describing a pitcher’s batted ball tendencies, you’re better off with GB% than GB/FB.

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Dave is the Managing Editor of FanGraphs.

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deadpool
15 years ago

Even then, GB% assumes all FBs are equal. Wagner’s a good example, when he’s at his best his GB% is very low, but his IFFB/FB rate is pretty spectacular. Somebody needs to come up with a good number that composites GB/FB with LD% and IFFB rates.

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