Surely, the new rules this year have significantly changed the baserunning landscape, and Ronald Acuña Jr’s stolen base total needs an asterisk, right? Let’s investigate, with focus on Acuña 2023 vs his prior career, and Acuña vs MLB at large.
*Disclaimer/credit: All numbers below are from Baseball Reference “Baserunning & Misc. Stats” tables, or are directly derived from the numbers in those tables. No shenanigans.
Ronald Acuña Jr has played 144 games through yesterday’s games (September 11), so I’m using 144 games as the baseline for this first data set, and all 2023-season numbers below are derived from numbers at this cutoff point of the season.
SB 2018-2022 vs 2023 per 144 games, Acuña vs all MLB Baserunners
| 2018-2022 Acuña: | 33.0 | 2018-2022 MLB: | 7.79 |
| 2023 Acuña: | 65 | 2023 MLB: | 11.48 |
| Increase for Acuña: | +116.8% | Increase for MLB: | +47.3% |
Both are up significantly, with Acuña’s up quite a bit more. But why? Do the rule changes somehow favor Acuña more than others?
SB Success Rate:
| 2018-2022 Acuña: | 77.0% | 2018-2022 MLB: | 74.2% |
| 2023 Acuña: | 83.3% | 2023 MLB: | 80.1% |
| Increase for Acuña: | +8.26% | Increase for MLB: | +7.98% |
This is basically a wash. Both Acuña and the league are up about 8%, so the rule changes clearly aren’t favoring Acuña any more than the league at large. Also, 8% isn’t much, and similar 1-year jumps over a previous 5-year stretch have happened before (as recently as 2007, but several times over the decades).
Yes, 2023 marks a new MLB record success rate, but so did 2021 and 2020, and 2007 and 2006, and 1996, and 1987 and 1985. (Before that the record hadn’t changed since the 1920s.) Base-stealing has become more efficient in recent years as more information about the value of steals has become available, and a new success rate record is set every few years for a variety of reasons. So, let’s look further.
SB Attempts per Opportunity
| 2018-2022 Acuña: | 15.4% | 2018-2022 MLB: | 4.8% |
| 2023 Acuña: | 25.55 | 2023 MLB: | 6.5% |
| Increase for Acuña: | +65.6% | Increase for MLB: | +34.5% |
Wow, okay. Acuña has turned it up almost twice as much as the typical MLB baserunner compared to their prior levels. But, still, base-stealing aggression is up significantly across the board. There’s nothing crazy or nefarious here. Acuña just wants it more.
SB Opportunities per 162 Games (to normalize to familiar numbers):
| 2018-2022 Acuña: | 285 | 2018-2022 MLB: | 245 |
| 2023 Acuña: | 344 | 2023 MLB: | 249 |
| Increase for Acuña: | +21.0% | Increase for MLB: | +1.43% |
Whoa! Base-stealing opportunities are very slightly up league wide, but Acuña’s stolen base opportunities are WAY up. (This ties in very nicely to his drastically reduced strikeout rate, while still making excellent contact. His 2023 BABIP is .335 compared to his prior career .333, so essentially no change there. He’s just putting many more balls in play with the same quality contact as before which, surprise, is resulting in a significantly higher batting average and on-base percentage.)
And that explains it. Acuña’s success rate hasn’t increased beyond any margin of error more than the rest of the league’s has, but he is getting on base a LOT more, and he is running a lot more when he is on base.
So, put your asterisk on stolen bases if you want. But for multiple reasons identified above, it would be a silly asterisk, and one that will never appear in any official recordbooks.
Like the article – thanks. I’m still putting a mental asterisk by RAJ’s SB totals, but that’s because I’m assuming that in 5-10 years they won’t look as unusual as they do now. I assume several players could (and will in the next few years) steal close to that many bases with that success rate if they tried, though many of them wouldn’t have RAJ’s OBP (even minus the HR & 2B) and so wouldn’t have his number of opportunities. It seems to me like RAJ should be one of the players with the least incentive to attempt steals, as the batters behind him are unusually likely to hit HRs, which would score him from first as easily as from second. Still, I imagine most teams have analytics departments capable of figuring out the odds and communicating them to the players, so I’m not sure why more players aren’t running more. I also worry about injury given RAJ’s history. All that said, if he can steal at an 80% rate in the postseason, that could be valuable, especially as the run environment may be lower (because of better pitchers in postseason games & perhaps also because of colder weather).
Agreed that RAJ should be one less likely to steal for the reason you mentioned: the lineup behind him can drive him in. But that’s part of my answer for why he’s stealing so many: he just wants it more. And, in his case, I’ve seen many times when he’s stolen second then scored on a single, and with the number of steals I have to think that’s contributing quite a bit in this particular season to his team-record-setting runs scored total.
Good point about the postseason. I didn’t think about that.
Another thing not mentioned: Just the threat of his stealing gets in some pitchers heads (not all), and any attempt to throw him out often results in less off-speed stuff and more fastballs. So Braves 2-3-4 hitters can generally really on more straight pitches to hit when Ronnie is on base…
Excellent write up. You guys may disagree and I would love your feedback, but it seems advanced metrics and especially basic metrics like OPS don’t capture the value of stealing bases. Could there be an alternate calculation for OPS that adds stolen bases less caught stealing to your slugging percent? Something like someone is 3 for 10 with 2 singles and a hr for a slugging percentage of .600. Let’s say he has 2 steals and 1 caught stealing. This would raise his slugging percentage to .700. I know if is very simple and probably totally off, but I don’t see the MVP talk fully considering the stolen bases.
The SB isn’t as valuable as a single, though, because it doesn’t advance any other runners (if they’re on). More importantly, the CS is a lot more costly than the base gained, because it both removes a baserunner and adds an out. At the least, you’d want to subtract the CS from the OBP. In extreme cases (like Davey Lopes, 47 SB/4 CS in 99 games in 1985, at age 40 no less), that might give a more accurate picture of a player’s value than just raw OPS.
Ronald’s base-stealing ability might be valuable in a playoff series against the Dodgers, as Will Smith (21%) and Austin Barnes (19%) have two of the lowest career CS%s among active catchers. (This is really a measurement of a combination of Smith, Barnes, and the pitchers who have thrown to them, of course, but the point is the same.) TdA is at 21% and Murphy at a still-not-great 27%, for comparison. Realmuto is at 34%.
What James said. Also, by and large, a runner needs to be successful more than 70% of the time for it to be worth the risk, and with so many home runs hit in recent years it might be closer to 80%. That “new knowledge” was a large reason for the decline in stolen base attempts in recent decades, and likely an indirect motivation for the rule changes this year.
Stolen base attempts are exciting, and if math says they aren’t as valuable as we once thought and they aren’t worth the risk if caught too often, then let’s do something that has a very small impact on game results but reintroduces some in-game excitement. Hence, this year’s rule changes.
What one has to remember in regards to caught stealing is it not only erases the base that would’ve gained from the steal, but also the bases that were gained by the PA and the other runners on base that are affected. For me, I’ve always looked at base stealing this way. With 65 steals and 13 caught, Acuna is stealing bases at an 80% success rate. So, Acuna has gained 65 bases while at least costing 26 AND adding an out. I’m sure the positive outweighs the negative, but probably not as much as we think it does.