The speed of the baseball off the bat, in miles per hour, measured at contact.
Exit velocity is how hard a ball is hit. It is one of the two Statcast inputs — along with launch angle — that most strongly separate batted balls that become hits and home runs from those that do not.
Average exit velocity is a useful but blunt summary; the share of batted balls hit hard (see hard-hit rate) and the quality of a hitter's best contact tend to be more predictive of power than the raw average alone.
Exit velocity underlies most contact-quality reads on the site. A hitter who consistently produces high exit velocity has more margin for a home run or extra-base hit than results-based stats alone suggest.
Individual batted balls of 95 mph or harder are classified as hard-hit. Hitters whose average and peak exit velocity sit well above league average tend to carry more power upside.