Yes, homers are up in 2023. They're way ahead of the comparable pace from last year, due to the cold spring/cold start that we experienced. But they're a little less than halfway back to 2021 levels at this point; still safely below the insane peak experienced in 2019.
We don't have the answer to the question of "why," either, but we won't duck the fact that such is the case. Instead, we'll show you what's currently happening in the ballparks (in terms of HRs per nine innings) as compared to last year's levels. These are the levels for the entire 2022 season, not the portion up to May 15th (which is what we have for '23: after all, the rest of the games haven't been played yet!).
And what that data tells us is that it's the American League parks that are driving the uptick. In the chart at right we've color-coded the parks by league: yellow for AL, green for NL. We've sorted them in descending order of increase--which shifts into those parks where homers have decreased at the line drawn betwee San Diego's Petco Park and Atlanta's Truist Park.
If you count up the parks on both sides of the line, you'll see that there are 11 AL parks that have seen HR/9 averages increase, while 9 NL parks have also done so. That might look like a fairly even increase across the leagues...but you should notice that of the 13 parks with the greatest percentage increase in HR/9 thus far in '23, 10 of them are AL parks.
Some tucking-in of distances seems to have shifted things in a big way at San Francisco's Oracle Park. Across the bay in Oakland, there were no dimension changes...just a sharp drop in starting pitcher quality on the woeful A's, which has brought their park closer to the league average from its usual HR suppressiveness.
We'd expect some convergence in this data as the season unfolds; next time we look at this (probably around the end of June), we'll retain the May 15th numbers for reference. Stay tuned--and keep swinging from the heels...
