In my last article, I discussed how baserunners have become more cautious, reflected in a decline in both stolen bases and taking extra bases on hits. I illustrated the conservatism when taking extra bases with graphs like this:

See what’s going on? Baserunners are less likely to go first-to-third on a single than they were 15-20 years ago.

To illustrate what’s going on with stolen bases, I used graphs like this:

Basestealers are succeeding at near-record rates (red bars), but they’re attempting far fewer steals (yellow line).

Out of curiosity, I decided to insert a yellow line like the one on the latter graph onto the first graph. Rather than try to explain it, let me show you:

Those red bars are the same ones I had at the top of this article. The yellow line represents the opportunities to advance from first to third on a single. And as you can see, they’re way down. To which I said: Huh? Stolen base attempts are down because managers are calling for fewer stolen bases. But the mere fact of a runner being on first when a single’s hit—that’s not strategy. That just happens. Why is it happening less?

Let’s explore the other opportunities to advance on a hit. Here’s a runner on first when a double’s hit:

Same story. There are a lot fewer times that there’s a runner on first when a double’s hit.

And a runner on second when the batter hits a single:

Again, those downward-sloping yellow lines don’t represent a strategic shift. It’s not something managers or coaches dictate, like stolen bases or sending a runner. Rather, something’s different in the way the game is played.

There are two ways this could be happening. Take runners on first when a single is hit. There could be fewer runners on first, or there could be fewer singles. Similarly, for runners going from second to home on a single, there could be fewer runners on second, or there could be, again, fewer singles. For runners with a chance to score from first on a double, there could be fewer runners on first or fewer doubles. Generally, there could be fewer runners on base, or there could be fewer hits with runners on base. Or both! We’ll see.

Let’s start with runners on base. Here’s a graph showing the percentage of plate appearances from 1996 to 2016 that occurred with a runner on first:

And with a runner on second:

So we shouldn’t be surprised that there are fewer runners trying to take an extra base on hits when starting on first or second, because there are fewer runners on first or second in the first place.

But why is that? Why has the frequency of runners on first or second declined?

There are a lot of ways a batter can get to first or second, of course. Let’s start with getting to first. The most common way is via a single. How’s that fared?

I added a trend line there, but it’s pretty obvious. Singles are down quite a bit. How about walks and hit batters?

Same story. As an aside, this is mostly due to walks; hit by pitch rates have remained historically high. If we combine the two, we get this:

For every 100 batters who got on base via a single, walk, or hit by pitch in 1996, only 92 did in 2016. That’s a big drop, helping explain at least part of why there are fewer opportunities for runners on first to go to third on a single or to score on a double.

Runners on second can get there by starting at first and getting advanced to second by a subsequent batter. Or they can steal second, which as I noted in the last article, was attempted in 2016 at the lowest rate in over 50 years. Or they can be advanced by one of those increasingly infrequent walks, hit batters, or singles. (Yes, I know there are other ways to advance a runner from first to second, but stay with me here.) Or they can hit a double:

Doubles are down too, but not by much. They’ve stayed in a pretty narrow band.

So here’s what appears to be going on:

  • There are fewer opportunities for runners on first to advance to third on a single, both because there are fewer runners getting to first and because there are fewer singles.
  • There are fewer opportunities for runners on first to score on a double primarily because there are fewer runners getting to first.
  • There are fewer opportunities for runners on second to score on a single, partly because the aforementioned lack of runners (who might get advanced to second) getting to first, but primarily because there are fewer singles.

Looking more broadly, fewer runners are getting on base via a single, walk, or hit by pitch, and there are fewer singles with which to advance them. How unusual is that? Well, we have a lot of data. Let’s look at the two-league era beginning in 1901:

There’s not much of a long-term trend there. Since World War II, the trendline’s almost flat. The recent dip in batters reaching first by a walk or hit by pitch is not unusual.

Same graph, with just singles:

Whoa. That’s a trend. The 2016 season was the first in baseball history in which singles occurred in fewer than 15 percent of plate appearances. The six years with the lowest rate of singles, walks, and hit batters as a percentage of plate appearances are, in order, 2015, 2012, 2014, 2016, 1968, and 2013. Or, in other words, the Year of the Pitcher and the past five seasons. But the driver is singles. The 20 seasons with the lowest rate of singles are, chronologically, 1965, 1967, 1998, and every single season since 2000. There have been 24 seasons in which there were more strikeouts than singles: 1965, 1967, and every single season since 1995. Or put another way, the 1994 strike season was the last one in which there were more singles than strikeouts. In 2016, there are more balks than singles.

OK, I made up that last one. But everything else with which I bludgeoned you is true. We’re seeing a lot fewer singles, resulting in both fewer runners on first who can take an extra base and fewer opportunities for runners on second to score on singles. So, as it turns out, there are two reasons why we’re not seeing baserunners take an extra base on hits as frequently as in the past. One is that they, or their third base coaches, are being more cautious. But the other is that there are fewer times when a runner’s in a position to take an extra base. And the reason for that is singles.

And what’s behind the decline in singles? Well, a lot of things. All-or-nothing uppercut swings. Better fielders. And, this one’s kind of risky—opens door a crack, yells SHIFTS, quickly closes it, locks it, and hides—well, if not shifts themselves, then better defensive positioning overall. Is it OK if I say that? A rocket down the line, a shot into the gap, or a ball hit over an outfielder’s head—those are going to be extra-base hits. Some singles are ripped as well, but there’s Crash Davis’s “gork, a groundball with eyes, a dying quail” and the proverbial past-a-diving-Derek Jeter grounders that a fielder positioned a yard or two differently might turn into a 6-3 or an F4.

The decline in singles isn’t a news flash. Joe Sheehan has been on this case for a long time. Of the 990 players who’ve accumulated at least 5,000 plate appearances in their career, the top 12 for fewest singles per plate appearance are mostly of recent vintage: Adam Dunn (last played in 2014), Gorman Thomas (1986), Carlos Pena (2014), Mark McGwire (2001), Mark Reynolds (active), Greg Vaughn (2003), Mickey Tettleton (1997), Jose Bautista (active), Dave Kingman (1986), Troy Glaus (2010), Barry Bonds (2007), and Dan Uggla (2015). Per at-bat, the top 12 are Thomas, Dunn, Pena, McGwire, Reynolds, Kingman, Vaughn, Jose Valentin (2007), Jay Bruce (active), Uggla, Glaus, and Ryan Howard (active).

So fewer singles is a well-established trend. But the ripple effects are significant. It doesn’t mean just that there are fewer runners standing at first, chatting with the first baseman or conferring with his first base coach. It also means that other exciting plays, including a runner advancing from first to third or from second to home on a single, are occurring less frequently as well.