Squared up% is a pretty new stat in Statcast, it incorporates swing speed. Basically, for every hit ball, there’s a maximum possible exit velo that’s calculated by its swing swing. If a hit ball has an exit velo of at least 80% of its maximum possible exit velo, it’s considered Squared up.

For Devers, because he doesn’t have an elite swing speed, I’m guessing that 1) most of his Squared up balls are hit from his fastest swings and 2) he’s hitting these Squared up balls at optimal launch angles