How Have the New Rules Changed the Game?

This is a big year for the MLB rulebook. After decades of tiny incremental changes, the league made three huge ones in 2023. They instituted a pitch timer, changed the size of the bases, and restricted defensive positioning for the first time in modern history. But how have these new rules changed how the game looks on the field? I broke down each one to find out.

Games Are Shorter

The biggest change to the game this year was the introduction of a pitch timer, and it’s had a huge impact on game length. Per Baseball Reference, the average nine-inning game has lasted two hours and 37 minutes this year, down from three hours and three minutes last year. You have to go back to 1985 to find a shorter average game length.

Despite that drastic change, the amount of action in a game hasn’t changed much. Plate appearances per game are roughly unchanged: there are 75.6 this year, quite close to the 76.4 average in the 21st century. Pitcher per plate appearance are stable: 3.9 this year, 3.9 for the last 10 years on average.

The difference is all pace. Per Statcast, pitchers are taking three fewer seconds to throw with the bases empty and 4.5 fewer seconds to throw with a runner on base. The bases-empty change is welcome but only gets us back to the numbers that prevailed 15 years ago or so. The change with runners on base is far more important; we’ve likely never seen a faster pace when pitchers are holding runners, though the data only goes back to 2010.

This faster pace matters for more than just time of game. It also matters for opposing baserunners, who now face fewer throws, fewer long freezes, and fewer intentional changes of tempo. There’s only so much you can do to disrupt a baserunner’s timing these days. Speaking of which…

Stolen Bases Are Up

You already knew this one. The larger bases and new limit on pickoff throws have combined to unleash a torrent of stolen bases not seen since the 1990s:

That graph tells a lot of the story, but the details are interesting as well. It’s not just a story of rampant running in the game; more importantly, runners are getting caught far less often. This year’s 79.6% stolen base success rate would be the highest mark on record, and a huge jump from the previous best rates in history. Note: a previous version of this article incorrectly characterized the late 1940’s as having high stolen base success rates. This was due to a data issue around caught stealing reporting and has been corrected in the chart below.

If you put two and two together, that means that the increase in stolen bases has handily outstripped the increase in stolen base attempts. Teams aren’t running at an unprecedented rate; they’re merely succeeding like never before. There are 1.78 stolen base attempts per game this year, a mark that has been eclipsed as recently as 2012. Every year from 1981 through 1997 featured more than two stolen base attempts per game.

As you’d expect, these steals are coming because of better leads, not worse throwing by catchers. Statcast calculates pop time for every stolen base attempt, so we can compare past years to the current one. It’s barely budged. In 2022, the aggregate league pop time on throws to second base was 1.98 seconds; this year, it’s 1.97 seconds. Catchers are getting the ball to second just as quickly, but that time simply isn’t enough anymore, thanks to the increased leads that runners can take.

What does that mean for run scoring? To a rough approximation, almost nothing. I tallied up how many runs were created by successful stolen base attempts, as well as how many were lost by unsuccessful attempts, by comparing the base/out situations before and after each attempt. This year, teams are adding roughly 0.07 runs to their per-game run totals thanks to steals. That isn’t much, and it’s an even smaller change from last year, when teams added roughly 0.035 runs per game thanks to the running game.

How much of a change is that? Run scoring is up by roughly 0.3 runs per game this year; teams scored 4.283 runs per game last year and 4.581 per game this year. Steals have accounted for 10% of that. The extra steals might make the game look different than it did in the past, but they haven’t done much to change the way it’s played at a fundamental level.

Pitch Violations Haven’t Mattered Much

While the pitch timer has had a huge effect on stealing, it hasn’t had much effect on balls and strikes. Pitchers and batters have both adapted to the new regime quickly, as you can see from our handy pitch violation leaderboards. Joe Musgrove leads baseball in pitch timer violations with six. That’s six pitches that automatically count as balls. Turned into run value, that works out to 0.2 runs he’s cost himself by holding the ball too long. That works out to roughly 0.06 points of ERA — and remember, that’s the pitcher who has been the worst at it.

If that effect sounds miniscule, it is. The Yankees have racked up 20 timer violations on their pitchers, the most in baseball. That’s 1.5 runs worth of free balls for their opponents. They’ve even gotten some of those runs back: opposing hitters have been called for five violations of their own, leading to free strikes. That’s just not much effect, even for the most frequent violators.

On the other side of the ledger, the Mariners have received 24 free balls while batting and been called for only four automatic strikes on their hitters. We calculate that difference as worth 1.3 runs of additional offense. They’ve scored 246 runs this year. The timer hasn’t done much to change teams’ fortunes; it’s merely kept the game moving.

BABIP Is Up, But Not Much

The shift is dead; long live the shift. One of 2023’s noisiest rule changes was a ban on infield shifting. Teams now have to place two infielders on either side of second base and with both feet starting on the infield dirt. The rule change was a counter to years of increasing overshifts; in 2022, lefties hit more batted balls into a shift than into a “normal” defensive alignment.

This year, lefties have hit exactly zero batted balls into an overshift. That’s been a tailwind when it comes to batting average on grounders. Last year, lefties hit .226 when they hit a ball on the ground. This year, that number is up to .236. They’re hitting their grounders slightly harder, but the main change is in defensive alignment. That said, the change also isn’t particularly impactful. As recently as 2017, lefties were batting .241 on grounders in a world of legal shifts. In 2021, lefties batted .232 on grounders. This isn’t much of a change.

Shifts help on more than just grounders, to be fair. Lefties have posted a .643 BABIP on line drives this year, up from an average of .619 from 2015 through ’22. That’s an extra handful of hits — 250 or so for the full season if line drive rates stay the same as last year. Every little bit helps, but we’re truly talking about little bits here. There’s not much chance of a huge, weather-based improvement, either. BABIP on grounders hit by lefties has ticked up slightly in summer months of recent years, but only by a few points:

Meanwhile, righties have barely been affected. As Tom Tango frequently notes, shifting against right-handed batters never made much sense. Now that teams can’t do it, not much has changed. Righties are batting .251 on grounders this year, as compared to .252 in that 2015–22 span. In other words, getting rid of the shift didn’t change anything when it comes to their balls in play.

The odds of things betting better for the offense don’t seem high. Teams are getting more data on how their new modified shifts work with every batted ball. Worst of all, the hits that the shift ban was supposed to resuscitate haven’t been happening. Grounders up the middle were hits since time immemorial before the shift got to them. From 2008 through ’14, which I roughly think of as the era before shifts went wild (my data starts in 2008), lefties hit .284 on grounders up the middle. From 2015 through ’22, they hit .239 on those balls; there was suddenly a defender standing there. This year, they’re hitting .243, because the shift restrictions just mean opposing shortstops stand behind second base.

If the league hoped to revive production on grounders, this set of shift restrictions looks like a failure. A wedge of space behind second base where no one can stand might do the trick, but merely requiring two infielders on each side doesn’t change the fact that teams now know that they can align their defenders based on hitter tendencies. You can’t put the toothpaste back in the tube; those singles up the middle always made sense to defend, and teams are now doing so even without the benefit of a full shift.

For the most part, I think MLB’s rule changes have been a success. The main observable change is tempo; games are lasting less time despite a similar amount of action. That’s a big change, and as measured by pitch violations, it hasn’t excessively affected any particular team or player. Instead, the game is just moving faster, which was the stated goal of the changes.

Changing the rules to increase stolen bases seems to have worked roughly as expected: Teams are running more frequently and with more success. Those steals aren’t making the game unrecognizable, though; we’re talking about an extra half a steal per game, give or take. I think there was reason to worry whether steals would become undefendable, but the evidence suggests that hasn’t happened. Catchers who control the running game are more valuable than in recent years, but that’s also hardly an unwelcome change. For the most part, I think that the extra steals leave the game looking like a slightly faster version of itself, just like the pitch timer changes.

On the downside, the new restrictions on infield shifts haven’t accomplished much of anything. Lefties are reaching base more frequently when they put the ball on the ground, but not at pre-shift rates. Defensive positioning is still taking hits away, particularly in the middle of the field. Righty batters still have a slight BABIP advantage on lefties thanks to infield positioning. If the league wants to fix that disparity, there will have to be stricter shift restrictions, probably centered around keeping the area behind second base empty.

If you were hoping for mostly the same baseball, congratulations: you’ve got it. If you were hoping for teams to start prioritizing speedy lefty singles hitters, or for batters to start trying to keep the ball on the ground to take advantage of the new defensive restrictions, that hasn’t panned out. Teams are scoring more this year, but that’s mostly unrelated to rules changes. I think that’s great; from my perspective, the league has threaded the needle by affecting how games look without putting their thumb on the scale of offensive and defensive balance.