Doubling Down

Image credit: © Wendell Cruz-USA TODAY Sports

If there have been two threads that have run through the last ten years of Major League Baseball, it’s been the surge in home run power and the surge in computing power. A decade ago during the 2014 season, levels of offense in MLB had sunk to their lowest levels in recent memory, dropping to 4.07 runs per team per game. This was still in the calling memory of the Silly Ball era of the mid-1990s and the 2000s. Even five years before in 2009, the average team had scored 4.61 runs per game.

In 2015, something odd happened. In the second half of the season, the ball started… behaving differently. Home runs began flying out of the ballpark in numbers that eclipsed even the Silly Ball era. An MLB investigation found that there had initially been unintentional differences in the composition of the ball that may have helped a few over the wall, but even after MLB (allegedly) put the ball back to normal, the home run barrage continued. The 2016 through 2021 seasons hold six of the top eight places among most homer-ful seasons in MLB history. The 2000 and, tellingly, 2023 seasons rounded out the other two spaces on that list. By the time 2019 came around, MLB teams were averaging 4.83 runs per game. Within a 10-year period, scoring in MLB had cratered and rebounded.

But now we see again a rapid decline in run scoring in 2024, as the run environment is back down to 4.32 per game as of Monday night. Worse than that, batting average is down to historically low levels, at .240 league-wide again as of Monday night (fourth worst mark on record) and an OBP of .311. There have been worse years there, but they all either start with 18, were in the dead ball era, or were in the late 1960s before the mound was lowered. Weirdly, home run rates are still doing well, with teams socking a little more than a home run per game on average, a rate consistent with the late 1990s.

There’s a very real way in which MLB offense is being propped up entirely by the long ball. There’s reason to believe that house of cards may be due for a crash as well. HR per fly ball, a decent proxy for how jumpy the ball is and a number that long held steady around 10%, but had ballooned to figures as high as 13-15%, has in the past few years taken a dive back to just over 10 percent.

While the home runs (and the attendant strikeouts) got all the attention, there was something else happening in baseball, hidden by the home run and strikeout surge. In the past decade, we lived through the shift wars. The now-forbidden strategy of placing three infielders on one side of second base was well on its way to overtaking the game. By the time it was banned, the shift was the default defense against left-handed hitters, with the majority of plate appearances taking place with a 3-1 split.

The shift was the most obvious way in which the modern analytic movement made its presence known. The logic behind it wasn’t all that hard to figure, but it felt a little icky. Hitters expressed frustration over a ball that had traditionally been a hit being gobbled up for an incongruous 5-3 ground out by a third baseman who was playing in short right field. League-wide BABIP, measuring how well defenses are able to handle balls hit into play, started to creep downward from a historical plateau of .300 to .290 in 2022. In 2023, with the shift banned, it was supposed to put more contact into the game as batters would be less afraid of a three-headed pull side. For a moment, it looked like it worked with BABIP rebounding to .297. But now it looks like 2023 was the outlier. League-wide BABIP has tumbled to .288 (again, as of Monday night).

What on earth happened? We seem poised at the edge of a new baseball ice age. What if I told you that there was a surprise villain in the room?

Warning! Gory Mathematical Details Ahead!

The conceit of banning the infield shift was that teams knew that some hitters liked to pull the ball and that’s why they shifted. It was a bit of a finger in the eye to the folks who were ready to challenge tradition with data, but it does seem to have “worked.” By forcing teams to pretend that they had no idea that your favorite lefty slugger liked to pull, BABIP on ground balls went up a bit in 2023 (and has stayed up in 2024). The effect has been about seven points in size.

Meanwhile, this happened:

That’s BABIP on air balls (line drives and fly balls) hit to an outfielder over time. As the analytic movement in baseball gained a toehold, then a foothold, and then a stranglehold on the game, BABIP in the outfield dried up, depending on where you want to date things from, to the tune of 20 points.

Here’s fly balls specifically:

That’s a drop of somewhere in the neighborhood of 40 points. Most fly balls get caught anyway, but there used to be a few more that fell in. The BABIP on line drive graph (not shown) drops similarly in that 2013 range to the tune of about 15 points.

What’s more important is what all those extra caught fly balls used to be. This graph shows the results of fly balls hit into the outfield over time.

Rates of balls dropping in for both singles and doubles have fallen, but starting around 2013, the effect was particularly harsh on doubles. That’s going to leave a mark. We’re used to talking about BABIP on the infield and usually that means singles, but outfield BABIP falling is going to have a bigger effect on offense.

There’s another graph you should see.

That’s the fate of line drives that made it to an outfielder’s glove. Outfielders are catching a lot more sinking liners than they used to and that’s drying up the supply of singles. And I can’t understate the importance of what you’re looking at in these graphs. The Domestic Horticultural Anti-Trespassing Brigade will tell you that the drop in batting average is because of a lack of solid fundamentals or contact hitting or something like that. Allow me to suggest an alternative theory.

The same forces that brought the infield shift about also were at work in the outfield. We know that outfielders routinely carry positioning index cards pre-programmed with optimal placements for each hitter. We see that during that 2013 era when so many other strategic things changed in the game, there was a sea change in outfield defense and importantly, it wasn’t just random variation. It’s been a new plateau. The effect was most visible on the infield because it looked weird to have three infielders on one side, but the idea of outfielders moving around a bit has never been controversial. Plus, it’s hard to notice with the naked eye that 16% of fly balls used to fall in and now it’s around 12. Most of the time, the ball gets caught. But when you think of it as 40 points of batting average, it takes on a more urgent meaning.

We can even specifically pin the tail on the little index card. I’ve been using Retrosheet data up to this point, but for a moment, I’m going to switch over to Statcast data. One of the many things that Baseball Savant does through the Statcast system is to calculate a catch probability for every fly ball. Catch probability is mostly based on how long the ball is in the air and how far the fielder has to go to get it. You can’t download that information on the plate appearance level, but they left enough public that I could calculate league-wide rates from 2016 to 2024.

Over the past nine years, catch probability has gone up in the outfield. One of three things is happening. Either batters are steering their fly balls closer to the outfielders (not likely), the balls are hanging in the air longer or the fielders are closer to where the ball lands more often. A graph of success rates (not shown) shows a similar upward trend in outfielders actually catching things.

It’s possible that the emphasis on hitting the ball upward means that the balls that don’t leave the yard are just staying in the air longer and are more catchable. It’s possible that better positioning is making it so that outfielders don’t have as far to run. Maybe both.

When banning the infield shift, MLB had some obvious landmarks (second base, the infield skin) to use in setting the rule. The outfield is just a big expanse of grass. If MLB wanted to regulate where outfielders stood, they would have to draw some chalk lines. But I’d submit that it was outfield positioning, rather than infield positioning that’s been the big mover on this one.

The only thing that covered for all of this was the ball becoming livelier and home runs spiking upward. Now the home runs are starting to dry up. Line drive singles and fly balls dropping in for doubles have been reduced. Hitters have probably gotten into some bad habits with respect to swinging too hard and pitching really has gotten a lot better in the meantime.

The optimist in me hopes that teams might react to the deflated ball by trying a more line-drive heavy approach, bringing more contact into the game that way, but the value in line drive contact has been cut down too. Hitters have to do something. But we know that they will pursue the best course of action to score the most runs that they can, even if run scoring might be down. And we learned last week that hitting the ball hard and collecting extra base hits is one of the best ways to do that.

But if we’re going to solve this issue, we’re going to need to acknowledge the elephant in the room who has snuck past everyone for the last 10 years. Outfield defense is playing a huge role in shaping the game.