The Boston Red Sox's bullpen has been stellar all season. Not only have they had the most dominant closer in baseball in Aroldis Chapman, their setup man, Garrett Whitlock, has been incredible too.
It hasn't just been those two, though; everybody in the Sox bullpen has played their role all season, leading to the Sox having the second-best bullpen ERA this season with a 3.47.
While a postseason appearance is not guaranteed at the moment, the Sox will control their own destiny over the final two series. Their bullpen will play a major factor over the next handful of games, helped by the fact that the expanded September roster has allowed them to carry one extra arm. Of course, when the playoffs come, the roster shortens back to 26 players; one pitcher will need to head to Fort Myers to stay ready to go, and won't be playing.
The Red Sox currently have the lowest bullpen ERA in the American League this season (3.45).
— nugget chef (@jayhaykid) September 16, 2025
The last time Boston led the AL in RP ERA? 2007.
The Sox's current bullpen carries five lefties and four righties. In all likelihood, all four righties (Whitlock, Zack Kelly, Greg Weissert, and Justin Slaten) will retain their spots on the roster. Chapman, Steven Matz, and Justin Wilson are all likely locked into their spots as well due to their successes this season and the different roles they provide.
One other factor is going to impact the playoff bullpen as well: the ability to shorten the rotation to four. Due to the extra rest days for traveling, it's possible to only need four starters and have all of them pitch with regular or extra rest. This allows for one extra arm in the 'pen than in the regular season. That leaves nine potential relief arms, but the Sox likely already have eight accounted for. That final spot is going to come down to three pitchers: Payton Tolle, Chris Murphy, and Kyle Harrison.
Which lefty reliever should remain with the Red Sox for their hopeful postseason run?
Payton Tolle
The rookie made a spectacular debut in the show, dueling (and, for most of the outing, out-dueling) the probable NL Cy Young winner, Paul Skenes. It hasn't been so great since that first start, though. Tolle was tagged for five earned runs in just three innings in his second start, two in two innings in his third, before being moved to the bullpen. While his first showing out of the 'pen was solid, his second wasn't nearly as good, being used in his first high-leverage chance.
The Sox think that his elite fastball will be effective in short spurts, but he has shown trouble commanding it at times. He'll need to have at least one more good outing to make his case for the postseason, but it doesn't seem like he's quite ready for the bright lights at the moment.
Chris Murphy
Murphy has been a very solid multi-inning relief option since returning from Tommy John surgery. He's been equally effective against both righties and lefties this season, holding lefties to a .619 OPS and righties to a .645. He has had some command issues in September, walking seven batters across his seven outings, while also allowing seven hits. The Red Sox have used him in more of a mop-up role this month as well, tending to use him when they are up or down big, but that is still a useful role in the playoffs.
Kyle Harrison
Harrison is the most versatile of the three arms at this point. While he's only made two appearances for Boston, they have both been really good. His first outing out of the bullpen was extremely promising, and then his second appearance, a six-inning start, showed why the Sox wanted him in the first place. The southpaw would provide both a multi-inning relief option and a potential spot starter if they needed him in the playoffs. The real question is, would the Sox pick him with so little experience with the squad over the other two?
In all likelihood, the Red Sox will go with Murphy, at least to start. He has the most experience of the three and can pitch multiple innings if the game gets out of hand, saving the rest of the bullpen for another game. There is too much uncertainty with Tolle at the moment to trust him in the playoffs. Harrison, being a starter, likely would start the playoffs on the taxi squad in Fort Myers, staying stretched out in case of injury. Murphy has proven himself this season to be a reliable option and could be a huge help in October.