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Could you help me understand the difference between the two? If a player has a px of 86 and an xpx of 107, how do I translate that
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Let's start with the definitions:
Expected Power Index (xPX)
2.6 + 269*HHLD% + 724*HHFB%
Previous research has shown that hard-hit balls are more likely to result in hits and hard-hit fly balls are more likely to end up as HRs. As such, we can use hard-hit ball data to calculate an expected skills-based power index. This metric starts with hard hit ball data, which measures a player’s fundamental skill of making solid contact, and then places it on the same scale as PX (xPX). In the above formula, HHLD% is calculated as the number
of hard hit-line drives divided by the total number of balls put in play. HHFB% is similarly calculated for fly balls.
Basically, PX is the "actual stat"... you get more PX by hitting doubles, triples, HR.Linear weighted power (LWPwr)
((Doubles x .8) + (Triples x .8) + (HR x 1.4)) / (At bats- K) x 100
(PX is LwPwr divided by League Avg LwPwr)
xPX is the "underlying skill". You get more xPX by hitting hard-hit line drives and hard-hit fly balls.
So, if your PX is below your xPX, it means you're hitting less extra base hits than we would expect based on the amount of hard-hit fly balls and line drives you've hit.
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