The vertical angle, in degrees, at which the ball leaves the bat after contact.
Launch angle describes the trajectory of a batted ball: negative angles are ground balls, low positive angles are line drives, and higher angles are fly balls and pop-ups. Home runs cluster in a sweet spot that is roughly in the mid-20s to mid-30s of degrees, paired with high exit velocity.
Launch angle on its own is incomplete — the same angle is a home run or a routine fly out depending on how hard the ball was hit. It is most useful combined with exit velocity, which is exactly what barrel rate and expected stats do.
A hitter who pairs a power-friendly launch-angle distribution with high exit velocity has a batted-ball profile that supports home-run and extra-base props more than batting average would imply.
Most home runs come on balls hit in roughly the mid-20s to mid-30s of degrees of launch angle, combined with high exit velocity. Angle without velocity, or velocity without angle, rarely clears the fence.