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What is HR/FB ratio? Definition and meaning of HR/FB (home run to fly ball rate) as part of our Sabermetrics glossary for fantasy baseball.
Welcome Rotoballers to our overview of HR/FB (home run to fly ball ratio). This article is a deeper dive into HR/FB, and is part of our ongoing series "Using Sabermetrics for Fantasy Baseball."
In this article, we'll explain why HR/FB is important and how short-term spikes generally aren't predictive of power breakouts in layman's terms that hopefully anyone can understand. We'll also look at how FB% (the percentage of a batter's batted balls classified as flies) can help fantasy baseball managers better predict HR totals.
You can find our entire sabermetrics glossary, which includes links to many other sabermetric stats as part of this series. Each stat deep dive will be released over the next few days. Stay tuned!
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What is HR/FB? Sabermetrics Glossary
Using BABIP to predict a player's batting average is great. Batting average is a category in many league formats, and every hit is an opportunity to steal a base or score a run. Most fantasy managers find the long ball sexier, though.
Every HR comes with a guaranteed run scored and at least one RBI. Many managers build their teams around power for this reason. Yet, fluky HR campaigns can happen as easily as fluky batting average ones. How do we tell the difference between a legitimate breakout and a fluke?
The answer boils down to two metrics: HR/FB (sometimes stylized as HR/FB%) and FB% (the percentage of a batter's fly balls vs. grounders or line drives). FanGraphs is the best place to find these metrics, though you have to scroll down to the fifth graph on each player's page (labeled "Batted Ball") to see it. Without further ado, let's review how to use HR/FB!
How to Interpret HR/FB Rate
HR/FB measures the percentage of fly balls that leave the park. In 2019, a power-friendly baseball contributed to 15.3 percent of all fly balls ending up in the seats. That number declined slightly to 14.8 percent in 2020 and 13.6 percent in 2021. In 2022, the decline continued with a league-wide mark of 11.4 percent. The league-wide HR/FB increased to 12.7 percent in 2023 but fell to 11.6 percent last year.
Like BABIP, an experienced player's benchmark is a better indicator of his future performance than the league average. For example, AL MVP Aaron Judge is generally regarded as one of the top sluggers in the game today. He slugged 58 HR last year, after all.
Judge's HR/FB was 32.2 percent in 2024. The Yankees would be in trouble if this number regressed to the league average. Fortunately, Judge crushed the league's HR/FB in every season of his career:
Above-average power is something Judge just does.
Large spikes or drop-offs in HR/FB are generally temporary, meaning the stat usually isn't predictive of a power breakout. Fantasy gamers want to find power breakouts, so this may be disappointing.
However, future power production may be predicted by an increase in FB%. There are limits here, as Jacob Young is never helping a fantasy team with his power no matter how many fly balls he hits. Still, FB% is generally the stat you want to look at for power potential.
What Is a Good FB%?
Elite sluggers generally post a fly-ball percentage of around 40. Subjected to this test, Judge had a 46.2 percent FB% in 2024, easily surpassing 40 percent. He should continue being a force at the plate so long as he keeps elevating baseballs.
Using the discrepancy between a player's HR/FB and FB% can be a great way to identify potential fantasy busts. Reading this column last year would have spared you from investing in Edouard Julien, who landed in the minors last season. It also would have warned you that Jesus Sanchez and Elly De La Cruz were both primed to disappoint in the power department.
Sanchez was a one-dimensional slugger who failed to crack 20 HR in 2024, so fantasy managers didn't want him. De La Cruz had a fantasy season for the ages, but he bumped his FB% by more than 10 points to do so (21.8 percent to 33 percent). Spikes like that are extremely rare and impossible to predict in advance.
We want to be as forward-looking as possible, and that means looking at 2024 data to identify potential busts for 2025. A few names that stand out include Christian Yelich (19.6 percent HR/FB, 26.5 percent FB%, Garrett Mitchell (29.6 percent HR/FB, 22.5 percent FB%), and Gunnar Henderson (23.9 percent HR/FB, 32.6 percent FB%).
It may be jarring to see a name as young and exciting as Henderson on this list, but remember that growth is always possible. If Henderson learns to lift the ball like Judge, his power output could explode. Still, you should consider the risk of a power decline before paying a premium.
Conclusion
HR/FB is considered the BABIP of power because it can be used to evaluate whether a given player is overachieving. A player with a large spike or decline in HR/FB should generally be expected to return to his established baseline moving forward. Ballpark factors may alter HR/FB, but in general, the raw fly-ball percentage is a better tool to identify potential power breakouts.
Of course, it is possible for a batter to legitimately change his approach and permanently boost his HR/FB. Statcast allows us to measure precisely how hard a player hits the ball, potentially validating a performance that would otherwise be a fluke. Check out later articles in this series for more information!
