Expected Batting Average (xBA): xBA measures the likelihood that a batted ball will become a hit. Each batted ball is assigned an xBA based on how often comparable balls — in terms of exit velocity, launch angle and, on certain types of batted balls, Sprint Speed — have become hits since Statcast was implemented Major League wide in 2015. By comparing expected numbers to real-world outcomes over a period of time, it can be possible to identify which hitters (or pitchers) are over- or under-performing their demonstrated skill.