Using BABIP to predict a player's batting average is great. Average is a category in many league formats, and every hit is an opportunity to steal a base or score a run. But most owners find the long ball sexier. Every HR comes with a guaranteed run scored and at least one RBI--and maybe more. Many owners 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?

HR/FB measures the percentage of fly balls that leave the park. Like BABIP, the league baseline is easy to remember at around 10%. Also 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, Giancarlo Stanton is generally regarded as one of the top sluggers in the game today. His HR/FB was 32.1% in 2015, more than triple the league average rate. If this number regressed to the league average, Stanton wouldn't be very good. However, he posted a 25.5% HR/FB in 2014, and enjoys a career rate of 25.9%. Clearly, above average power is something Stanton just does. Last year was perhaps a little better than his norm, but he has clearly proven to be a superior slugger.

Large spikes or dropoffs in HR/FB are generally temporary, meaning that the stat is usually not predictive of a power breakout. Fantasy owners want to know the next power breakout, so this may be somewhat disappointing. Future power production may be predicted, however, by an increase in fly ball rate, or the percentage of a batter's flies as opposed to liners or grounders. Elite sluggers generally post a fly ball percentage of 40% or higher. Subjected to this test, Stanton had a 44.9% rate in 2015, 39.1% in 2014, and a career mark of 40.1%. These rate stats, combined with a consistently above average HR/FB, make Stanton the player he is.

Stanton doesn't really illustrate the distinction between HR/FB and FB% because he excels at both. For a predictive illustration, consider his teammate Christian Yelich. His HR/FB last season was 12.5% - 25% better than a league average showing. This would seem to indicate an above average power season. Yet he managed only seven big flies in over 500 PAs last season. The reason is a tiny 15% flyball rate, a rate too low to do anything with even Stanton's power.

To conclude, 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. The league average hovers around 10%, and a given player's past performance is a better indicator of future performance than the generic league baseline. A player with a large spike or drop off in HR/FB should be expected to return to his established baseline moving forward. Ballpark factors or a major change in offensive approach may permanently alter HR/FB, but in general raw flyball percentage is a better tool to identify potential power breakouts. This may seem to indicate that batters want to hit nothing but flies, but that is not always the case. We'll look at why in Part 3 of this series, batted ball distribution.

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