Ronald Acuña Jr. and the fight to trust Baseball Savant's Baserunning metric

Ronald Acuña Jr. is having an historic season on the basepaths, but metrics don't seem to indicate that.

New York Mets v Atlanta Braves
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Ronald Acuña Jr. is on the cusp of becoming the first player in MLB history to hit 30 homers and steal 60 bases in a single season... with a month to go in the season. There's a high probably he steals 70 bases, which hasn't been done by a Brave since 1991, and there's even a long shot of a 40/70 season, something that makes Eric Cole shutter to hear.

However, if you were to look at any baserunning metric, you'd see that Ronnie ranges from being above average to simply being average. For most Braves fans, this would seem shocking. After all, not only is he stealing bases at an 85% clip, but he's also still doing things like scoring on a sacrifice fly to 2B.

So what's going on?

Why do baserunnning metrics hate Ronald Acuña Jr?

They don't, but they are lower on Acuña than even I would expect. After all, Ronnie leads all of baseball in steals, and he's doing it at a success rate that's 5% above the league average. That would generally indicate a really great baserunner.

But Acuña is currently ninth in baseball in Fangraphs' BsR with a 5.4 BsR, exactly half of the MLB leader Corbin Carroll, and is 119th in Baseball Savant's Baserunning.

Baseball Savant and Fangraphs have different formulas to calculate baserunning ability. Baseball Savant does not include base-stealing while Fangraphs' does, but FanGraphs doesn't have public access to the weight of an individual baserunning decision, which Savant does.

Fangraphs combine uses a score for stealing bases (wSB), taking extra bases (UBR), and avoiding double plays (wGDP) to create BsR.

Unsurprisingly, Acuña does lead the league in wSB with 6.1. However, the metrics believe that he either hasn't been aggressive or hasn't been successful (or both) at taking extra bases and only has a UBR of 0.4.

What's really hurt Acuña is the number of double plays he's grounded into. His wGDP is -1.1. This isn't abysmal, as Carlos Correa has a wGDP of -4.4, but it isn't great.

Should the ability to avoid double plays, especially when you hit a ton of hard ground balls, be factored into your base running abilities? It's debatable, but that's the way Fangraphs does it.

Baseball Savant doesn't grade stolen bases at all, which makes the potential NL MVP look a lot worse on the bases than he really is. But I also mostly agree with the ratings. After all, they are calculated by people much smarter than I am.

The scoring on the sacrifice fly that I showed you at the beginning gave him 0.25 for advancing safely. A lot of risk on a ball so shallow, but is rewarded for scoring.

Unfortunately, Ronnie's been thrown out at home twice. This is the worst one, getting -0.83 runs credited.

What's hurt Acuña the most, however, is simply not advancing at all. Most I can get on board with. This double by Ozzie Albies was hit with one out, but it was far enough that Ronnie should have been able to score. He was hit with -0.12.

He also has several -0.01 and -0.02 for not taking the extra base as a batter or a runner. Could he have turned this into a triple? Probably, but is it worth getting thrown out? Probably not.

However, there are a few incidents where I disagree with Savant.

A few minor disagreements with Baseball Savant Baserunning

There are a few examples where I think Savant either penalizes Acuña too harshly or penalizes him when he should be penalized at all. This wouldn't skyrocket Ronnie to the top of the leaderboard, but it would get him out of the zeros.

April 17 @ SD: -0.20 for not trying for a double

I don't think penalizing him for not reaching 2B is the wrong decision, but I do think the weight of it is harsh. It's one of the higher penalties for not advancing without being thrown out, and in this single, the Padres' RF had it backed up perfectly.

If this was a -0.05 penalty, I don't think I'd dispute it, but I'm pretty confident Acuña's only hope of reaching 2B is if he was sprinting at top speed out of the box.

April 14 @ KC: -0.19 for not advancing to 3B from 1B

This should've already been overridden. This single was initially called a foul ball, and after review, the umpires placed Olson at 1B and Acuña at 2B. This ended up getting Brian Snitker ejected.

Getting penalized for where the umpires place you is ridiculous.

July 5 @ CLE: -0.19 for not turning a single into a double

Mike Petriello disagrees with me on it, so frankly you should probably side with him, but I'm still going to include it. Ronnie smokes this ball at 113.1 MPH off the bat and Steven Kwan barehands it on one bounce before making a great throw back in.

The broadcast says that Acuña wasn't running super hard off out of the box, but he's still running out of the box and he takes a hard turn around 1B.

Should this be a penalty? Probably? Most balls that hit off the wall should be a double, especially if you have Ronnie's speed. Was it -0.19 runs worth by not making it to 2B? I'd argue it would be slightly less.

What to make of the metrics?

Ronald Acuña Jr. is going to do something historic this season on the basepaths. His ability to steal bases has been incredible, even with the bigger bases.

However, the metrics are probably closer to being right than wrong. There are definitely parts to nitpick, but overall, the Braves superstar hasn't been quite as aggressive in non-stolen base opportunities as he has in past years.

Part of that might just be because he knows he needs to preserve his legs. Why take risky advances where you could get thrown out, or worse, injured? The part is that he could know he could steal anyway. After all, when you can just do this, why not just steal?

The metrics don't think Acuña is a bad baserunner because he's not, they just recognize that the bulk of his value is coming from steals, while other players gain value in other areas.