For context, these expected stats come from taking basic information about an individual batted ball—such as exit velocity, launch angle and the ballpark where it was hit—and comparing that to past data to determine the most likely outcome. But the key bit here is the data used to make those comparisons. The league calculates the baseline for that twice per year, according to MLB stats analyst Mike Petriello: once at the All-Star Break and once more after the end of the season. This means that before the All-Star Break—like, say, right now!—the baseline actually comes from past years.
Yes, this is all very wonky, (literally) inside-baseball stuff. But it’s crucial to understanding what these numbers are saying. In other words: When you see there was basically no league-wide gap between expected and actual stats in 2021 and 2020, you’re seeing there was basically no gap once the baselines had been adjusted to reflect the offensive environment for those years, which has not yet happened for 2022. In a world that didn’t have any dramatic, year-to-year swings in offensive environments, this wouldn’t mean too much. Unfortunately, MLB is clearly not in that world. If there’s a big change in the offensive environment from one year to the next—for instance, if the baseball itself is different—the numbers will show notably different things.