How MLB’s New Rules Changed the Game in 2023

Which rule changes worked best (and least): Here's a weekly helping of Brain Food to make you smarter.

Baseball has had no shortage of interesting storylines this season, from the individual excellence of Shohei Ohtani, Ronald Acuña Jr. and Mookie Betts to the dominance of the Atlanta Braves and the expensive failures in New York and San Diego. But one of the most important moments of 2023 didn’t happen on the field — nor did it even happen in 2023.

Last September, MLB’s competition committee voted to adopt a comprehensive set of rule changes, including a pitch clock, a ban on infield shifts, larger bases and restrictions on pickoff attempts. These new rules, which were first implemented at the major-league level in February for spring training, have set the tone for the entire season in ways both predictable and surprising.

Let’s go through each new policy to find the biggest takeaways from Year 1 under baseball’s new paradigm.

Pitch clock

The rule: Pitchers have 15 seconds between receiving and delivering the ball with bases empty, and 20 seconds with runners on.

Key metric: Average time of game dropped from 3:03 to 2:39.

This was the centerpiece of the rule changes, intended to speed up the game and create a more watchable product. Heading into 2023, MLB brass predicted that the average length of a game could drop by about 25 minutes based on pilot programs in the minor leagues — and that’s pretty much what happened. Compared with 2022, the average game was 24 minutes faster, and the number of nine-inning games that went three-and-a-half hours or longer dropped from 231 last season to just 9 this year. Any fears that players would struggle to adjust to the new pace were also put to bed by the fact that per-pitch violation rates dropped by 63% between April and September.

But as successful as those topline numbers are, the change did seem to gradually lose effectiveness over the course of the season. The average length of a game was 2:36 in April, rose to 2:40 by July, and was 2:44 in September, with the share of games completed in under 2:30 dropping from 35% early in the season to 23% by the end.

None of this is back to 2022 levels, of course. But since postseason games tended to be about 15% longer than regular season games under the old setup, it’s possible the pace of play will be even slower next month.

Shift ban

The rule: Defensive alignments must include two fielders on each side of second base with both feet on the dirt at the time of the pitch.

Key metric: Lefty hitters’ batting average on ground balls rose from .226 to .239.

After being used on 38% of all plate appearances in 2022, including 62% against left-handed hitters specifically, the defensive shift — much-maligned by both batters and fans of symmetrical baseball aesthetics — was mostly nerfed for 2023. (I say “mostly” because 22% of plate appearances this season saw batters “shaded” just barely within the rules, the new version of shifting.) The change was predicted to improve leaguewide batting average — which had fallen to its lowest point (.243) since the Year of the Pitcher in 1968 — and to particularly help out lefty sluggers, many of whom saw their careers destroyed by the shift.

The rule clearly seems to have worked in those aspects. Batting average is up to .249 overall this season, with averages on balls in play rising from .290 to .297. Batting average on ground balls is up from .241 to .248 overall, including a big 13-point leap for lefties specifically.

Without those annoying fielders in odd places, more balls have snuck through for hits. Of course, as a side effect of the shift ban, MLB also hoped that batters would be encouraged to put more balls in play, but that part is still a work in progress. The overall number of balls in play per game actually dropped slightly from 2022 (24.4) to 2023 (24.3), and the share of plate appearances ending in one of the “three true outcomes” — i.e., home runs, walks and strikeouts, plays where the fielders have no influence — rose from 33% to 35%.

Perhaps this will change with more years to strategize around the new rules, but for now the shift ban has only succeeded in turning more of those balls in play into hits, not in producing more balls in play as well.

Limited pickoffs and larger bases

The rule: Bases increase from 15 to 18 square inches in size. Pitchers are limited to two “disengagements” (i.e., pickoff throws or step-offs) for each plate appearance.

Key metric: Successful stolen bases per game increased from 0.51 to 0.72.

As I wrote on Wednesday, the running game is officially back in MLB. In addition to steals per game increasing by 41% year-over-year, MLB also set a new single-season record for stolen base success rate at 80%, breaking the old record of 77% from 1914. This success rate had been increasing in recent years anyway — in 2021, base-stealers were successful 75.4% of the time, the highest rate since 1916 — but it was on a comparatively low volume of steal attempts. Without the benefit of the new rules, it’s unlikely a new record would have fallen, while attempts per game also rose by 32%. Furthermore, 2023 can boast baseball’s most prolific league-leader in steals since at least 2010 — and possibly longer, if Acuña Jr. can swipe a couple of extra bags in the next few days.

In contrast with the pitch clock, which has begun to see its effect wear off over time, there isn’t a clear sign that pitcher-catcher batteries got any better at stopping runners as the season progressed. September has seen the highest rate of stolen base attempts (0.97) and successful steals (0.78) per game of any month, and MLB’s collective stolen base success rate since July (81.2%) is higher than it was through June (79.3%).

Because of all this, it might be fair to call the rules encouraging more steals the most unqualified success of all MLB’s new initiatives. The only counter-argument might be that there still was a surprisingly low correlation between teams’ stealing effectiveness and actually winning ballgames … but rules changes can only do so much.

Brain Food is our weekly serving of data that will make you a smarter sports fan. Have a tip for something you want me to write about? Email or tweet X me at npaine@themessenger.com or @Neil_Paine.

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Filed under: Baseball