Intersting Article from Mike Petriello

https://www.mlb.com/news/takeaways-mlb-opening-week-2023

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1. BABIP is up! Maybe. It's weird
With the shift limitations in play, the idea was that a few more batted balls would turn into hits, and not nearly as many would find their way into the gloves of fielders who were positioned in spots that they generally were not for much of baseball history. So, is it working? Maybe.

BABIP stands for Batting Average on Balls in Play, or batting average without including strikeouts or home runs, with the idea just being "how often do balls in the field of play turn into hits." As you'd expect in a shift-limited world, it's a little higher this year. It's .294, up from the .282 it was in 2022's first week. While it didn't stay at .282 all year long it landed at .290 let's try to keep it "first-week based," to get closer to an apples-to-apples comparison. Which was the point. Fantastic.

Here, though, is where it gets weird.
A) It's up by more for righties than lefties. Didn't see that one coming, did you? In the first week of 2023, righty BABIP jumped by 14 points, from .286 to .300. But lefty BABIP has gone up by only 9 points, from .276 to .285.
B) Lefty ground ball BABIP is barely up at all. This is the fascinating part. Last year, in the first week, lefties managed a meager .214 BABIP on grounders. This year, it's all the way up to … .218. Grounders weren't terribly successful in the past, and they won't be now, either fielders are just too good.
But that doesn't mean there's been no impact, either, because look at this:
C) Lefty line drive BABIP is up by a lot. A LOT. In last year's first week, lefty liners led to a .607 BABIP, because line drives are extremely valuable hits. In this year's first week, lefty liners have led to a .656 BABIP, which is a pretty massive increase. It would be the highest full-season number since 2013, which is basically right before the shift took hold across the Majors.
Why is this? It's too early to say for certain, but it might be early confirmation of something that seemed to be noticeable during Spring Training, which is that there was too much focus on "you can't have three infielders on one side" and not enough focus on "and the two infielders you have must each be on the dirt, not in the grass."

You can see this playing out in the data just by looking at how deep fielders are playing or, more accurately, aren't playing. In each of the last two seasons, second basemen (with lefty batters up) played an average of 156 feet deep. This year? It's 146 feet deep, and having to stand 10 feet closer to the batter isn't a minor difference.

And as for those grounders?
"There's no worse feeling than hitting the ball hard up the middle and seeing the shortstop standing right there," said Eric Hosmer this winter at Chicago's fan convention.
Up-the-middle ground ball BABIP for lefties currently sits in a tracking-era (since 2008) low. Those probably aren't ever coming back.

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These are good metrics (BABIP, and more specifically BABIP for ground balls and line drives) to keep an eye on as the season progresses

The stats I really want to see:

In extra innings, how many of the free runners score without benefit or a hit or any mistake by the defense (error, wild pitch, passed ball, balk, etc), and how often is that the deciding run?

I just have a fundamental objection to a team (and the advantage in extras is even bigger for the home team now) being able to score without a hit and without having done anything to earn that runner on the bases.

So I guess that might be a third stat: does the free runner on second base change the home-visitor win balance in extra innings?