Home Runs per Fly Ball (HR/FB)
Description:
The ratio of how many home runs are hit against a pitcher for every fly ball they let up. Home runs are obviously not a good thing for a pitcher to let up and a pitcher can reduce the number of home runs hit against them two ways: by increasing their GB% against and lowering their FB% or by reducing their HR/FB ratio. While pitchers can control to an extent the type of batted balls hit against them, there is some luck involved in whether a pitcher lets up a ball hit into the seats or to the warning track. For example, pitchers that throw in a home ballpark with short fences will tend to let up more HR/FB than pitchers that throw predominantly in expansive ballparks. HR/FB rates have also been shown to vary considerably from year to year, meaning they have little predictive value.
Context:
League average HR/FB rate is 10.6%. Since it’s been proven that HR/FB rates are not very predicitive, xFIP uses this value when estimating a player’s HR/FB rate. Players actual HR/FB rates fluctuate around this average, ranging anywhere from around 4% to 16% on a year-by-year basis.
Things to Remember:
- Taking a glance at a pitcher’s HR/FB rate can help tell you if a player got lucky or unlucky over a season. Pitchers with HR/FB rates much higher or lower than league average will tend to regress towards league average in the future, which will have a corresponding effect on their ERAs and FIPs.
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