Fly Balls and Groundball Pitchers

In today’s Hardball Times, Matthew Carruth did an analysis on extreme groundball pitchers and how they do not really give up more home runs-per-fly ball (HR/FB) than your typical pitcher. There has been some thought that extreme groundball pitchers do tend to give up more HR/FB because they’re only allowing fly balls when they throw a bad pitch, thus making it easier to hit the ball out of the park. Carruth’s analysis even suggests that the opposite might be true, though the correlation was quite weak.

I decided to run a similar analysis using data from 2002 to the present. The average HR/FB rate during that same period is 10.7%. If we look at the 2002-present totals of all pitchers with a groundball percentage (GB%) greater than 55% and more than 100 innings pitched, they have an average HR/FB of 12.2%. That 12.2% is not a weighted average, it’s just a simple average of each qualified pitcher’s HR/FB.

Using the same method, if you look at pitchers with a GB% less than 35%, they have an average HR/FB of 9.9%.

Now I’ll admit this is a much simpler approach than the route Carruth took, but the results seem to be considerably different and I wondered why this would be the case.

First off, if you use my approach with the 20 pitchers Carruth selected in each group, you come to the same conclusions as Carruth did. This leads me to believe the batted ball data from Retrosheet (which Carruth used) and the batted ball data from Baseball Info Solutions don’t quite match up.

Just taking a quick look at the top 10 players, their GB% don’t match. For exampe, Retrosheet has Brandon Webb with a GB% of over 70% and BIS has him at 65%. That’s the first difference.

The second difference is that the time period he used was between 1988 and 2006 where the HR/FB according to Retrosheet was 13.57%. This is considerably different than the HR/FB of 10.7% that Baseball Info Solutions reports between the 2002-present time period. Using the 13.57% for all pitchers over a 18 year period where there’s been some considerable influx in home run totals is probably going to cause some issues as well.

To me it seems there is at least some evidence that extreme groundball pitchers as a group do give up more HR/FB than your typical pitcher. The two most extreme groundball pitchers in the past 5 years have an average HR/FB of 15.5% (Brandon Webb) and 13.1% (Derek Lowe).

The other option is it really has nothing to do with GB% at all (sampling size issue maybe?) and it’s just that some extreme groundball pitchers tend to have higher HR/FB. In their case instead of regressing to the league average, you’d just regress to the player’s actual average; treating it more like you’d treat a batter’s batting average on balls in play (BABIP) than you would a pitcher’s BABIP.

David Appelman is the creator of FanGraphs.

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17 years ago

David, are your stats based on home runs per outfield fly, or total flyballs (including infield flies?). Sorry for forgetting, but THT’s are based on outfield flies only.