On Effectively Wild episode 857, which aired April 7, former Baseball Prospectus staffer and founding member, and current Sports Illustrated and newsletter writer, Joe Sheehan discussed the emergence of 12- and 13-man pitching staffs, and how they’ve hurt offense by both creating the one-inning relief specialist and reducing the number of hitters on the bench. This has had several trickle-down effects on the game, including, according to Joe:

Comebacks are less likely, not just because the relievers are better but because the hitters are worse.

As it turns out, on the same day, Russell Carleton posted an article about comebacks on BP, in which he concluded

Baseball isn’t dead yet, and the numbers show that even in the era of having 5 guys in the pen who all throw 98, the comeback isn’t a lost art.

So who’s right? Are comebacks less likely or are they the same as it ever was?

Well, if you ask me, they’re both right! The chart below displays the percentage of games won by teams trailing after six, seven, and eight innings over the past 30 years.

As you can see, the percentage fell, but arguably imperceptibly, from 1986 to 2014. During the five years from 1986 to 1990, teams trailing after six innings came back to win 13.36% of games. During the five years from 2010 to 2014, the winning percentage fell, but only to 13.02%. That difference equates to a little over a half a win per 162 games. For teams trailing after seven innings, the trailing team came back 9.15% of the time in 1986-1990, and 8.83% in 2010-2014–again, a difference of about half a game per 162. And teams trailing after eight innings have fared no worse, winning 4.77% of games in 1986-90 and 4.81% in 2010-2014. So on that basis, things have been pretty stable. As Russell explains in his article, bullpens are better now, but starters are better as well, which means that late-inning leads are smaller, and therefore more surmountable, than they were in the past. So comebacks aren’t down.

But comebacks fell off a table last year. I chose the years 2010-2014 rather than 2011-2015 in the prior paragraph for a reason. Teams trailing after six innings won only 11.8% of games last year. Teams trailing after seven won only 7.5%. Those trailing after eight won 3.5%. Each of those figures represents the lowest winning percentage for trailing teams over the last 30 years, the latter two by a margin of about 0.7%. That’s a meaningful drop. Joe’s view, that large bullpens of one-inning relievers both suppress offense and leave managers with fewer bats on the bench to deploy strategically late in the game, seems to have taken hold.

So who’s right? It’s pretty foolhardy to make a call based on just one season of data, unnerving though 2015 may have been. However, stormclouds do seem to be gathering. For comebacks when trailing after six innings and when trailing after seven, the three toughest seasons have been 2012, 2014, and 2015. That’s not true of comebacks when trailing after eight, but last season’s 3.5% is 17% lower than the previous low-water mark. So far this year, teams have come back in an above-average 17.8% of games in which they’ve trailed after six and 10.2% of games in which they’ve trailed after seven. But it’s just the middle of April, and many bullpens aren’t yet settled. It’ll take a few more months before we have the data to tell whether Joe or Russell is right about comebacks.