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.