Let’s look at some potential homerun decliners based on the following “Power Score” or expected homerun (xHR) formula and compare it to their actual homerun totals. Here is the formula:

Plate Appearances(PA)*Contact Rate(Ct%)*Outfield flyball rate(OFFB%)*Homerun per Outfield Flyball ratio(HR/OFFB).

Make sense? Sure it does: How many homeruns does a player hit per outfield flyball? How much of their contact results in an outfield flyball? How much overall contact does a batter make when swinging the bat in a plate appearance? This should provide us with an expected HR total.

The below lists are ranked by the largest actual HR-expected HR differentials. Their HR related performance (PA, Ct, OFFB, HR/OFFB) is listed along with their average homerun and flyball average distance and rank.

Two contingencies worth noting at this time: 1) Our samples size still isn’t huge and 2) We’re not taking into account platoon hitters, i.e. Scott Van Slyke as a right-hand hitter only raking against left-hand pitchers. So when I extrapolate the data, keep this in mind. In other words, if Scott Van Slyke consumed more playing time against right-hand pitchers, there’s a good chance his performance/power would drop off.

Here are the top potential HR decliners (I think you will see the value of this xHR comp immediately):