Home Run to Fly Ball rate (HR/FB) is the ratio of how many home runs are hit against a pitcher for every fly ball they allow. Home runs are obviously not good for a pitcher, and a pitcher can reduce the number of home runs hit against them in two ways: by increasing their ground ball rate (therefore lowering their fly ball rate), or by reducing their HR/FB ratio.
While pitchers can control (to a certain extent) the type of batted balls hit against them, there is less skill involved when considering whether a long fly ball is hit into the seats or to the warning track. For example, pitchers who throw in a home ballpark with short fences will tend to have a higher HR/FB ratio than pitchers who throw in large ballparks. Pitcher HR/FB ratios have also been shown to vary considerably from year to year, meaning they have limited predictive value.
Please note that the following chart is meant as an estimate, and that league-average HR/FB rate varies on a year-by-year basis. To see the league-average HR/FB rate for every year from 2002 to the present, check the FanGraphs leaderboards.
Remember, extreme home run rates in either direction are likely unsustainable. Certain pitchers can consistently post lower than average home run rates, though, so if trying to determine if a pitcher’s HR/FB rate is unsustainable, be sure to also compare it to their career rate.
Things to Remember:
● Taking a glance at a pitcher’s HR/FB ratio can help tell you if a player had an over- or under-inflated ERA. Pitchers with HR/FB ratios much higher or lower than league average will normally regress towards league average in the future, which will have a corresponding effect on their ERAs and FIPs.
● One limitation of the HR/FB ratio is that home runs can also come off of line drives. Generally speaking though, the main principles and implications of a pitcher’s HR/FB ratio remain the same.
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