As much as the Red Sox' search for a top-of-the-rotation starter will dominate headlines, the effort to fortify the march through the late innings looms as large, and perhaps as a greater challenge. After all, the Sox bullpen was by many measures the worst in the majors last year, with the absence of Koji Uehara and late struggles of Junichi Tazawa leaving the team bereft of the sort of strikeout-per-inning arms that have become a staple of the game.
Red Sox relievers finished with a 4.24 ERA last year. The league average bullpen had a 3.71 mark. What are the odds of bridging that divide of 0.53 earned runs per nine innings?
Excellent, actually. The hallmark of bullpens is their inconsistency. The Mariners offer a compelling microcosm, having gone in the last four years, from a 3.39 ERA in 2012 to a 4.58 ERA in 2013 (rise of 1.19 runs) to a 2.59 ERA in 2014 (drop of 1.99 runs) to a 4.15 ERA (rise of 1.56 runs) in 2015.
While that's an extreme snapshot, it's far from isolated. Over the last 10 years, there are 30 instances of teams whose relief ERAs changed by at least one run – with 16 of them representing improvements by at least a run and 14 representing declines of at least one run. On average, teams saw their bullpen ERA change by 0.52 runs on a season-to-season basis over the last 10 years – meaning that a "normal" ERA adjustment could give the Sox at least an average bullpen, and with the possibility that it would be far from an outlier for the team to improve by, say, a full run, which would in turn suggest a bullpen that had gone from a weakness to a strength.
Of course, the theoretical ability to improve a bullpen's performance isn't the same as rolling a host of 7's in a row to achieve a drastic improvement. The Sox' biggest one-year improvement of the last decade came between 2006 and 2007, when the relief ERA dropped by 1.41 runs en route to a championship primarily thanks to a) lightning in a bottle with the signing of Hideki Okajima; b) a breakthrough by Manny Delcarmen in middle relief; and c) drastic defensive improvement that permitted a bullpen group with modest strikeout numbers to record outs.
The lesson? Bullpen improvement can happen even without adding a single "name" relief arm. That said, there's a considerable amount of luck involved in getting the sort of performances from unheralded relievers that allow a bullpen transformation.
"What you really try to do is . . . project some people's performance taking a step forward, through scouting and analytics, and try to go that way," president of baseball operations Dave Dombrowski said on WEEI's Hot Stove Show this week. "Other than premium guys that are your premium closers, there's so much inconsistency in bullpen performances throughout the years. So the good arm just doesn't settle, because you can have a good arm and still get hit. … I think sometimes you have to look at the year before. Was somebody overworked? Were there any injury factors? You have to look at all of those things and hopefully make wise decisions that end up working for you."
Dombrowski said he's already made one decision in the hopes of achieving improvement in the late innings, committing to Matt Barnes as a reliever entering spring training. Beyond that? It's an offseason notable for the lack of elite free agent relievers, meaning that even in an area where dramatic improvement is possible, the path to achieve it is, for now, obscure.