One of my crusades the past few years has been against the misuse of a couple of the newfangled metrics. Both average exit velocity and average spin rate are misleading, since they encompass contributions from multiple components. Yet many, including yours truly, use the aggregate metric to support an argument which may be untrue since one of the components tells a different story.
More also doesn’t always mean better. For instance, spin rate affects pitches differently. For this example, I’m ignoring that not all spin is useful, as that’s a topic for another day. In simplified form, spin aids side to side movement while pitches designed to drop don’t need spin since gravity is doing the work. Someone like Hyun-Jin Ryu doesn’t show up high when sorting by average spin rate, since spin isn’t desired for most changeups. That said, backspin on a four-seam fastball counteracts gravity, fooling the hitter with its perceived rising action.
One of the assumptions made with batters is exit velocity helps batting average. Statcast average exit velocity (AEV) is used to judge if a BABIP is due for regression, good or bad.
Yet, there are a plethora of hitters with below average AEV but high xBA (expected batting average). Sure, some is due to better contact rates, but there still appears to be a disconnect. How can he continue to hit for average with such a low AEV?
Before going further, keep in mind Statcast xBA compares the specifications of every batted ball (EV, launch