Exit Velocity measures the speed of the baseball as it comes off the bat, immediately after a batter makes contact. This is tracked for all Batted Ball Events — outs, hits and errors.
Attaining a high Exit Velocity is one of a hitter’s primary goals. A hard-hit ball won’t always have a positive result, but the defense has less time to react, so the batter’s chances of reaching base are higher.
For this very reason, Exit Velocity can also be used to evaluate pitchers (known as “Exit Velocity Against”). The game’s best pitchers — who naturally throw the highest quality pitches — generally rank among the league leaders at limiting hard contact.
Average Exit Velocity (aEV) is calculated by dividing the sum of all Exit Velocities by all Batted Ball Events.