Expected slugging uses the same Statcast foundation as xBA but predicts total bases instead of just hits. Every batted ball is assigned an expected total-base value based on exit velocity and launch angle, and xSLG is the per-at-bat average.

xSLG is where raw power shows up most clearly. A hitter who consistently hits the ball 108+ mph at 25-degree launch angles will have a high xSLG even if some of those drives got caught at the warning track. The quality of contact is there — the results will follow.

The gap between actual SLG and xSLG is one of the most actionable signals in baseball. Large positive gaps (xSLG > SLG) suggest underperformance that will correct. Large negative gaps (SLG > xSLG) suggest the hitter is getting lucky on batted balls and the power numbers will come back down.

What is a good xSLG?

xSLG feeds into xwOBA, which is used to calculate xNUT. It captures expected power output — hitters who barrel the ball consistently will have high xSLG even if a few warning-track flyouts temporarily suppress actual SLG.

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