Expected Slugging Percentage (xSLG) is a highly accurate measure of power hitting. It’s formulated using actual exit velocity and launch angle. In contrast to Slugging Percentage (SLG), xSLG removes defense and park factors from the equation. Hitters and pitchers are able to influence exit velocity and launch angle but have no control over what happens to a batted ball once it is put into play. To calculate xSLG, each batted ball is assigned an expected result (single, double, triple, home run) based on results of comparable batted balls since 2015 and weighted.
Here is the major league leaderboard in xSLG for starting pitchers (350+ plate appearances):
10. Sonny Gray (CIN) – .341
9. Kente Maeda (LAD) – .338
8. Noah Syndergaard (NYM) – .336
7. Gerrit Cole (HOU) – .334
6. Stephen Strasburg (WAS) – .334
5. Jacob deGrom (NYM) – .331
4. Charlie Morton (TBR) – .327
3. Max Scherzer (WAS) – .322
2. Blake Snell (TBR) – .321
1. Luis Castillo (CIN) -.314
Note the gap between Castillo and Snell is the largest gap on the leaderboard. Sonny Gray starts tonight against the Cardinals and Luis Castillo goes tomorrow.