HR/FB: Using Sabermetrics for Fantasy Baseball

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.

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 just 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% (or what percentage of a batter's batted balls are fly balls as opposed to grounders or line drives). FanGraphs is the best place to find both of these metrics, though you will have to scroll down to the fifth graph on each player's page (labeled "Batted Ball") to see it. Without further ado, let's get started!

How to Interpret HR/FB

HR/FB measures the percentage of fly balls that leave the park. In 2019, a power-friendly baseball contributed to 15.3% of all fly balls ending up in the seats. That number declined slightly to 14.8% in the shortened 2020 season, and declined further to 13.6% last season. The league benchmark used to be 10%, but stronger players and bouncier baseballs probably won't let the league's HR/FB get that low again.

Like BABIP, an experienced player's personal benchmark in the stat is a better indicator of his future performance than the league average. For example, AL MVP Shohei Ohtani is generally regarded as one of the top sluggers in the game today. His HR/FB was 32.9% in 2021, significantly higher than the league-average rate. If this number regressed to the league average, Ohtani wouldn't be very good. However, he has a career rate of 29.4%. Clearly, above-average power is something Ohtani just does.

Large spikes or dropoffs in HR/FB are generally temporary, meaning that the stat is usually not predictive of a power breakout. Fantasy gamers want to know the next power breakout, so this may be somewhat disappointing. Future power production may be predicted, however, by an increase in FB%. There are limits here, as Billy Hamilton 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, Ohtani had a 40.6% fly-ball rate in 2021. That passes! It also explains why Ohtani smashed 46 HR after never previously producing at a 30-HR pace in the United States, as his career FB% is just 33.2%. While Ohtani improved his HR/FB slightly, the real difference was that he hit a lot more fly balls and put his always outstanding raw power to better use. 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 DJ LeMahieu and Eloy Jimenez, both of whom finished the season as a bust (though Jimenez was partially health-related). You also would have missed out on another solid season from Tim Anderson, and this author has no idea how he does what he does.

We want to be as forward-looking as possible, so that means we have to look at 2021 data to identify potential busts for 2022. A few names that stand out include Jared Walsh (25.4% HR/FB, 29.9 FB%), Josh Bell (25.5% HR/FB, 26.5 FB%), and Juan Soto (24.4% HR/FB, 28.7 FB%).

It may be jarring to see a name as big as Soto's on this list, but remember that power is only one path to fantasy value. Soto needed 654 PAs to hit 29 long balls last season, 41st in baseball. He's elite because of his batting average and OBP with power, not because he's a pure power threat. That said, he could also be one of the biggest beneficiaries of elevating more baseballs like Ohtani did last year.

Conclusion

HR/FB is considered the BABIP of power because it can be used to evaluate whether a given player is outperforming his true talent level. 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, 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 is hitting the ball, potentially validating a performance that would otherwise be labeled a fluke. Check out some of our other introductory sabermetric articles for more information!

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