Bullpen Usage Is Destroying Offense This Postseason

The story of this postseason has been the dramatic change in the attitude towards relief pitcher usage. It’s been most notable in Cleveland, where Andrew Miller has been used anywhere from the 5th through 9th inning, but basically all of the teams still left have been utilizing their best relievers as often as possible, and relying more on their bullpens than ever before.

Yesterday, over at FiveThirtyEight, Rob Arthur showed that this isn’t just our perception, but that teams really are pulling their starters earlier than ever this year. Below, I’ll borrow a neat graphic from his post.

The maxim of starting pitching being the key component to winning in October is dying a very public death this month; relievers are the hot new thing, and pretty much everyone is buying in at the same time. But in Arthur’s piece, he also suggests that this big change hasn’t actually mattered all that much.

But is this shift to the bullpen working? No — or at least, not that we can see.

Runs per game tends to decline from its regular season norm every October, and this year is no different. So far, only 2.6 runs per game are crossing the plate in the postseason, down from 4.5 in the regular season. If managers’ newfound bullpen savvy was depressing runs per game to a significant degree, you’d expect the gap between the regular season and postseason to be even larger than usual. But that’s not the case: Since 2000, seven years have seen larger drops in scoring between the regular season and playoffs than we’ve seen so far this year.

Another place reliever usage might alter the game is in terms of preventing comebacks. Going to the bullpen while the starter is cruising is an even tougher sell when you have a lead, but sabermetrics suggests it’s the best way to preserve that lead. Through 24 playoff games3, there have been two comeback wins after six innings — close to the regular-season average of 13.6 percent. Similarly, if managers were acquiring leads and then unleashing a cavalcade of relievers to prevent offense, we’d expect there to be less movement in win probability. But the 2016 postseason has featured an average win probability change almost exactly in line with those of previous Octobers.

That part of the article struck me as odd, as it certainly feels like offense is way down this October, and that relievers are primarily responsible for the domination of opposing hitters. So, instead of just looking at runs per game, I asked David Appelman to send me the regular season and postseason wOBA for each of the last 15 years. Here’s those numbers in a table, along with the difference between the two.

As I write this, hitters are posting a .278 wOBA this postseason, the lowest year of any year in the sample, down 14 points from last year’s postseason, even though offense was up during the regular season this year. And naturally, that means that the gap between regular season and postseason wOBA is at its largest point in the sample as well. Here’s a graph of the data, in case you’d rather see it visually.

The broader recent trend has been towards larger gaps in wOBA between the regular season and postseason, with 2016 being a more extreme version of 2010 and 2012, the previous years where there were gaps over 30 points. This lines up a bit with Arthur’s graph of the move away from starting pitching, and it’s probably not a coincidence that gap is getting larger as starters are being asked to pitch less in the playoffs.

So why isn’t it showing up in runs per game yet, as Arthur noted yesterday? Well, run scoring can be influenced pretty heavily by sequencing, and especially in small samples, stringing hits together can lead to runs even if pitchers dominate most of the rest of the game. But when we look at the rate stats that are the building blocks of offense, we can see pretty clearly that offense is down significantly this postseason, and manager’s increased aggressiveness in using their relievers is indeed working.