Batted Ball Data (ground ball, fly-ball, and line-drive rates) presents the percentage of each batted ball type hit against a pitcher. Much like how hitters have partial control over their batted ball splits, pitchers do have some control over the way the ball is put into play against them. Depending on their pitching philosophy, pitchers can tend to be primarily ground ball or fly ball pitchers.
Pitchers with high ground ball rates tend to give up more total hits, but they also allow fewer extra base hits. This is relatively intuitive: ground balls are harder to field than fly balls and they rarely go for extra bases (and almost never go for home runs). So pitchers who limit the amount of fly balls hit will also limit the amount of extra bases against them. Similarly, fly ball pitchers tend to allow fewer total hits, but more extra base hits.
There are a few other interesting side effects to pitchers have extreme batted ball profiles. This is taken from the SIERA page, as SIERA uses batted ball data in its formula:
In general, ground balls go for hits more often than fly balls (although they don’t result in extra base hits as often). But the higher a pitcher’s ground ball rate, the easier it is for their defense to turn those ground balls into outs. In other words, a pitcher with a 55% ground ball rate will have a lower BABIP on grounders than a pitcher with a 45% ground ball rate. And if a pitcher walks a large number of batters and also has a high ground ball rate, their double-play rate will be higher as well.
As for fly balls, pitchers with a high fly ball rate will have a lower Home Run Per Fly Ball rate than other pitchers.
Please note that the following chart is meant as an estimate, and that league-average batted ball rates varies slightly on a year-by-year basis. To see the league-average batted ball breakdown for every year from 2002 to the present, check the FanGraphs leaderboards.
Ground ball pitchers generally have grounder rates over 50%, while fly ball pitchers have fly ball rates above (or approaching) 40%.
*Infield pop-ups are also tracked on FanGraphs (IFFB%), and they are expressed as the percentage of pop-ups a batter hits out of their total number of fly balls.
Things to Remember:
● Line drives are death to pitchers, while ground balls are the best for a pitcher. In numerical terms, line drives produce 1.26 runs/out, fly balls produce 0.13 R/O, and ground balls produce only 0.05 R/O.
● This data is tracked by Baseball Info. Solutions (BIS), which is why it’s only available for players back until 2002.
Links for Further Reading: