Introduced before the 2017 season, Hit Probability is a Statcast metric that measures the likelihood that a batted ball will become a hit.
Each batted ball is assigned a percentage based on how often comparable balls have become hits since Statcast was implemented Major League wide in 2015, using exit velocity, launch angle and, on certain types of batted balls, Sprint Speed. (As of January 2019, Hit Probability now factors in a batter's seasonal Sprint Speed on "topped" or weakly hit" balls.) For instance, a line drive to the outfield with a Hit Probability of 70 percent is given that figure because balls with a similar exit velocity and launch angle have become hits seven out of 10 times since the implementation of Statcast.
Barrels -- a metric introduced in 2016 -- have a combination of exit velocity and launch angle that results in a minimum Hit Probability of 50 percent, though the Hit Probability of the average Barrel is much higher (82 percent).
Why it's useful
Hit Probability tries to get to the heart of what a pitcher and hitter control while attempting to take out the effects of defense and ballpark. Setting aside foot speed for infield hits, a batter's impact on whether the ball was a hit or an out ends as soon as the bat makes contact. Likewise, a pitcher cannot control what happens to a batted ball after it leaves the bat.
With knowledge of the probable outcome of each batted ball, an expected wOBA can be created for each player -- factoring in non-contact figures like a player's strikeout and walk rates.
Watch: Statcast measures the Hit Probability of round-trippers belted by the Brewers in a six-homer game.