A massive spike in bullpen usage has been one of the defining factors of modern baseball, and the Yankees have positioned themselves to take advantage.
They are around the middle of the pack in terms of bullpen usage, but they have made the most of these innings and lead the majors in bullpen ERA (2.78) and strikeout rate (11.6 per nine innings). Their relief corps got even stronger this week with the addition of Zach Britton, who pitched a scoreless eighth inning in Thursday night’s 7-2 win over Kansas City and is two seasons removed from posting a 0.54 ERA with the Orioles.
It likely has never been more important than now to have a strong bullpen, given that the relievers’ share of innings has reached a new high.
Coming into Thursday, bullpens have accounted for 39.2 percent of all innings pitched, which would break the all-time mark of 38.1 percent that was set last year. This uptick is not an outlier, as a record for bullpen usage has been set every year since 2015.
Yankees manager Aaron Boone said facing fresh relief arms is tough on hitters, and this helps explain the trend.
“It is a challenge when you’re facing two, three, even four guys in a game,” he said before Thursday night’s game. “There’s certainly something to that and it has been fascinating how we’ve really seen the bullpen evolve over the last three, four years [and] 10, 15, 20 years as well.”
This rate of bullpen usage has more or less been increasing gradually since about 1920, when relievers threw just over 17 percent of the innings. Bullpen usage exceeded 25 percent for the first time in 1948 and cleared the one-third mark in 1995. From then until 2014, the rate stabilized somewhat and bounced between 32 and 35 percent, before growing again the past three seasons.
“I’ve been a GM for 21 years and the evolution of how a pen looks now is a lot deeper and stronger than it’s ever been,” Brian Cashman said Thursday afternoon. “I do, every now and then, wonder what it’s going to look like in a few years.”
While it might make some traditionalists squeamish, it is not hard to see why this strategy is appealing to teams. Relievers are generally more effective at retiring hitters and preventing runs, as they do not have to worry nearly as much about in-game fatigue or familiarity with hitters.
This season, relievers have a 4.04 ERA compared to a 4.22 ERA for starters, and this gap is actually atypically narrow (the average difference during the past 20 years is about 0.37 runs).
The split is even more pronounced later in games. Batters came into Thursday hitting .268 in their third plate appearance against a starter, according to Baseball-Reference.com. Contrast this with their .242 average against relievers.
Yankees relievers came into Thursday having thrown 39.1 percent of the team’s innings, which ranked 16th, one slot below the Mets (39.3 percent). Only four seasons ago, both rates would have led the majors.