BA − xBA
Actual batting average minus expected batting average — a luck gauge.
What BA − xBA means
Positive means more hits than the quality of contact earned, usually via placement, speed, or friendly defense. Large gaps in either direction tend to close over the following weeks.
How BA − xBA is calculated
BA − xBA
Also written
ba_minus_xba · avg_xba_gap · babip_luck
Source
Statcast