MLB rule changes and preseason stats

We know that at least one of the major rules changes is changing the shape of spring training games. Pitch clocks have made pace of play significantly faster with an average game time of 2 hours and 39 minutes. While I am quite excited about the prospect of snappier baseball games, I wanted to dig into the other changes a bit and see how different the games might look in all respects for the coming season. First, an over simplified version from Jeff Passan:

Stolen bases have been one of the major talking points of the pitch clock/limited pick off attempts/larger bases rules. We are expecting more players to be aggressive on the base paths, and so far that is what we are seeing, but I think the second article I linked above is underselling the affect. Sure the success rate and attempts are a few percentage points higher, but it is much starker in nominal terms.

If you go pull the 2022 versus 2023 team stats, teams are stealing .0097 more bases per plate appearance, and the average team has been caught stealing .00019 more times per plate appearance. At least on average, teams are stealing more and being caught more, but most people would look at those numbers and write them off as too small. If scale those up through current total played however, that equates to 155.7 more stolen bases and 3 more caught stealing attempts, which is a rather stark difference. The Royals have been contributing to the stolen bases, they are slightly above the median in increasing SB/PA over last spring, but they have gotten caught less often than last spring.

Success happening at a rate of 50 to every additional failure is a startling shift in how teams are going to approach base running. The original hate toward stolen bases that came with early Sabermetrics was really based around run expectancy based on success, failure, and the probabilities of the coming hitters in different out situations. If the success rate goes up enough, run expectancy will become positive in many more situations, so expect the analytically advanced teams to quantify this and find a lot more times to take advantage. It will not change the run environment a ton, but an extra 0.75 or so stolen bases per game times a value of around 0.2 runs would be 0.15 extra runs scored per game, about 364.5 per year roughly.

After looking at stolen bases, I moved on to seeing if the shift rules were doing anything. I have never seen a study in how shifts are used in spring versus the regular season, so I am not how aggressively teams shifted even last year when there were no restrictions. It seems to me they would be less interested in min-maxing run expectancy in the spring and showing teams how they planned to shift them come the regular season. Jeff Passan’s stat above suggests that theory might be wrong with ground ball BABIP increasing by more than 20 points. However, when I look at overall BABIP rates, the average team BABIP has only risen by .0073, and only 18 out of 30 have higher BABIPS than last spring. That is not enough teams to be conclusive. The Royals are one of those teams. They are currently at .385 versus .371 last spring.

The sheer number of factors that can nudge BABIP up and down coupled with not knowing the shift differences between spring and regular season in both past and present seasons makes me think we should wait until April to start seeing how this rule change will play out. The expectation is that ground balls, especially hard hit balls from lefties to the right side, are going to be hits more often. That is a very narrow set of balls in play, so I am not entirely sure what sort of sample size will be needed to know that any differences are real. For now I think the safe bet is to assume that we know nothing.

I am probably the most excited I have been going into a baseball season since maybe 2015. The games look like they are going to be faster and have more stolen bases, while the possibility of more balls in play versus three true outcomes is still there. MLB may finally be moving toward the more spectator-friendly experience they have been talking about for years.