Batted Ball Statistics are fairly straightforward: they express the share of a pitcher’s balls in play that are line drives, ground balls, or fly balls. This includes balls that leave the park (home runs), so the sum of a pitcher’s batted ball statistics should be 100%. Major league pitchers feature a variety of pitches and approaches, resulting in different batted ball profiles. Some pitchers allow lots of fly balls, others allow lots of balls on the ground, and many others fall somewhere in between.
Infield pop-ups are also tracked on FanGraphs (IFFB%), and they are expressed as the percentage of pop-ups a pitcher induces out of their total number of fly balls. These numbers are generally small and fluctuate from year to year, but they’re the best type of batted ball for pitchers, as they almost always lead to an out (in fact they count as strikeouts in WAR).
The statistics published on FanGraphs are drawn from data from Baseball Info Solutions (BIS) and reflect the share of a pitcher’s total balls in play that are of a certain type, classified as line drives, fly balls, and ground balls. Fly balls are also divided up between infield fly balls and total fly balls. To wit, the following are the formulas to calculate the percentages you can find on the site:
Line Drive Percentage (LD%) = Line Drives / Balls in Play
Fly Ball Percentage (FB%) = Fly Balls / Balls in Play
Ground Ball Percentage (GB%) = Ground Balls / Balls in Play
Infield Fly Ball Percentage (IFFB%) = Infield Fly Balls / Fly Balls
Our batted ball data goes back to 2002, but it’s important to remember that there is no perfect way to define each type of batted ball so some balls that you might consider a fly balls might get classified as line drives and vice versa. In reality, batted balls exist on a continuous distribution from rolling perfectly on the ground to being launched straight up in the air. The cut points between the three classifications are somewhat arbitrary and imprecise, so do not treat the data as infallible.
Why Batted Ball Stats:
Batted ball stats are extremely useful for determining the type of pitcher at which you’re looking. There is no ideal batted ball distribution, but pitchers who allow a lot of line drives typically perform worse than pitchers who allow lots of fly balls or ground balls. Generally speaking, line drives go for hits most often, ground balls go for hits more often than fly balls, and fly balls are more productive than ground balls when they do go for hits (i.e. extra base hits). Additionally, infield fly balls are essentially strikeouts and almost never result in hits or runner advancement. Here are the numbers from 2014:
We use these stats to tell us two things. First, we want to get a sense of a pitcher’s style of play. A ground ball pitcher is usually someone who doesn’t allow a lot of extra base hits, but gives up a fair share of singles and features a two-seam fastball or sinker quite often. A fly ball pitcher will often give up fewer hits, but that might include more extra base pop, including home runs. These pitchers tend to rely more on four-seam fastballs up in the zone.
Additionally, batted ball data can tell us something about a pitcher’s underlying performance. We often look at a pitcher’s Batting Average on Balls in Play (BABIP) to make determinations about the sustainability of their performance and batted ball data informs that analysis in an important way. If a pitcher allows a lot of line drives, a high BABIP is more likely a function of his true talent than a pitcher who allows a lot of fly balls, who has probably just been unlucky in running that higher BABIP. Generally, ground ball pitchers will run higher BABIPs than average and fly ball pitchers will run lower BABIPs than average.
We know that pitchers do not have complete control, or even much control at all, over what happens to a baseball once it’s put in play, but they do have some control over the type of batted ball they allow. If you allow ten ground balls, you can’t control if zero, three, or nine go for hits, but you did control the fact that none are leaving the park. On the other hand, fly ball pitchers can usually limit the number of hits they allow, but that also makes them more vulnerable to home runs.
Batted ball numbers allow us to dig deeper into the kind of pitcher a guy is and how responsible he is for the outcomes of balls in play. No pitcher is completely responsible for their BABIP, but we can get an impression of how legitimate the current number is by looking at their batted ball profile.
How to Use Batted Ball Stats:
Batted ball statistics, like most statistics, should be used with caution for three key reasons. First, sample size is very important for line drive rate, and while you can get a good sense of fly ball and ground ball rate with a month or two of data, it takes more like a year and a half for line drive rate to “stabilize.” All this means is that six weeks of batted ball data shouldn’t change your opinion of a player’s talent level with respect to hard contact. Generally, we care more about grounders and fly balls for pitchers than line drives because we’re interested in the type of pitcher they seem to be. That stabilizes more quickly, but can still fool you in small samples.
Second, batted ball classification is tricky. What’s the difference between a fly ball and a line drive? At what angle does one become the other? While BIS has a great team scouting each major league game, video data only offers only a certain level of detail. Even the most diligent stringer can’t get it right 100% of the time because they just don’t always have the proper angle to distinguish between a fly ball and line drive. When StatCast becomes fully operational, this problem should disappear because we will be able to use a simple numeric cut point.
Finally, and most importantly, not all line drives/fly balls/ground balls are created equally. A pulled fly ball traveling at 105 mph to deep left field and one that lands harmlessly in the glove of the right fielder are extremely different. A screaming line drive up the gap and one that’s easily caught by the shortstop are different. This is essentially another example of the data being a continuous (in launch angle, direction, and velocity) but presented as discrete data. A ball isn’t a fly ball or a line drive, it is hit at X launch angle, Y degrees from center, at Z velocity. Essentially, use batted ball stats as a guide, not an anchor.
Our categorization is helpful, but it is far from perfect. For example, in 2014, Brandon Crawford and Anthony Rizzo had very similar batted ball statistics, but Rizzo was clearly the better hitter overall as the quality of his contact within those categories was much better than Crawford’s. This is true for pitchers as well. There are pitchers that allow weaker contact than others even if they have the same batted ball profile.
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.
This serves as an important reminder that while we can get a general idea about a pitcher from their batted ball profile, a fly ball against Clayton Kershaw isn’t the same thing as one against Joe Blanton in most cases.
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%.
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.
● A line drive produces 1.26 runs per out, while fly balls produce 0.13 runs per out and ground balls produce 0.05 runs per out. In other words, batters want to hit lots of line drives and fly balls, while pitchers generally want to cause batters to hit ground balls.
● Players that don’t allow many balls in the air (higher GB% with lower FB% and LD%) generally have higher BABIPs and batting averages against, but allow fewer extra base hits.
● GB/LD/FB% are calculated per ball in play.
● IFFB% is per fly ball.
Links for Further Reading: