Exit velocity

Exit velocity is the speed of a batted ball at the instant it leaves the bat, measured in miles per hour by camera- and radar-based tracking systems installed in professional ballparks. It is a direct physical measurement rather than a derived statistic, and it is one of the core inputs behind modern batted-ball analysis.

On its own, exit velocity says only how hard a ball was hit; paired with launch angle, the vertical angle the ball leaves the bat, it becomes far more predictive of outcome. Balls hit in the "barrel" zone, a specific combination of high exit velocity and a launch angle roughly between 8 and 32 degrees, historically produce a batting average and slugging percentage well above average, and this pairing underlies expected-outcome stats such as expected batting average and expected weighted on-base average.

Teams and broadcasters use exit velocity to separate hitters who consistently make hard, well-struck contact from those with similar traditional stats but weaker contact quality that may not hold up, since hard-hit rate tends to be more stable season to season than results-based numbers affected by batting average on balls in play luck and defensive positioning. The pitfall is treating exit velocity alone as predictive: a ball crushed straight at a fielder or hit on the ground can still produce a weak outcome despite high exit velocity.