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.
Context:
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.
| Rating | HR/FB |
|---|---|
| Excellent | 5.0% |
| Great | 7.0% |
| Above Average | 8.5% |
| Average | 9.5% |
| Below Average | 10.5% |
| Poor | 11.5% |
| Awful | 13.0% |
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.
Links for Further Reading:
Platoon Splits, BABIP, and HR/FB rates – FanGraphs
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