Following another second half collapse, the Red Sox bullpen is due for a massive shakeup.

Kenley Jansen and Chris Martin, the club’s top two relievers over the past two years, are both free agents. So are trade deadline acquisitions Luis Garcia and Lucas Sims. Jansen seems like a lock to sign elsewhere, and it’s not clear if any of the other three will return.

Though the Red Sox will have high-leverage options to turn to — more on that below — it’s clear the club needs to bring in some additional firepower to make sure the bullpen can hold up over an entire season. With the pitching staff as a whole skewed heavily towards right-handers, finding a dominant lefty would be an added bonus.

Fortunately, one of the best left-handed relievers in baseball is set to hit free agency next month: Tanner Scott.

Over the past two seasons Scott has established himself as arguably the top lefty reliever in the sport. He’s proven capable of shutting down right and left-handed hitters, and also that he can handle a huge workload without breaking down as the season goes along.

Simply put, he checks every box for the Red Sox, who are now positioned such where adding a high-octane arm like him wouldn’t just be a good investment, but a necessary one.

State of bullpen

While the bullpen should look a lot different next year, a lot of the key pieces are already in place. Liam Hendriks will be back after completing his recovery from Tommy John surgery, and rookie Justin Slaten established himself as a high-leverage weapon who could one day contend for a closer role.

Garrett Whitlock will also most likely move back to the bullpen upon his return from elbow surgery, a role in which he’s previously thrived.

Behind those three stalwarts, the Red Sox have accumulated a huge amount of depth. Greg Weissert was Boston’s most heavily used pitcher in 2024 and enjoyed an outstanding finish after spending about a month in Triple-A. Zack Kelly was often dominant, but also inconsistent.

Brennan Bernardino was a borderline All-Star in the first half before completely falling off down the stretch. Cam Booser bounced back and forth from Worcester but generally pitched well. Luis Guerrero didn’t allow a run in nine appearances following his September call-up, and Zach Penrod flashed potential in limited action, too.

Isaiah Campbell and Chase Shugart remain in the mix, and Michael Fulmer, Wyatt Mills and Chris Murphy could be wild cards once they complete their recoveries from elbow surgery.

If we assume at least one bullpen spot will go to a long reliever — let’s say Cooper Criswell — then the Red Sox will have more than enough bodies to fill the bullpen even if they don’t make any additions and allow all of their free agents to walk. So much like with the starting rotation, if the Red Sox want to take things to the next level, they don’t need to tinker with the margins. They need someone who can plug in right at the top.

What sets Scott apart?

Since the start of 2023, no lefty has been as consistently overpowering as Scott. He’s posted back-to-back seasons with at least 70 appearances and sub-2.50 ERAs, and his 7.6 WAR over that stretch is by far the most in MLB by a left-handed reliever.

This year he enjoyed his best season, posting a 1.75 ERA with 84 strikeouts over 72 innings while tallying 22 saves. He also earned his first career All-Star nod, and since being traded midseason from Miami to San Diego he’s established himself as a key weapon in the Padres bullpen.

He’d only made one postseason appearance prior to this season, but so far he’s met the moment. Entering Friday’s decisive Game 5 he’d posted four consecutive scoreless appearances to start the playoffs.

Scott’s advanced metrics are also off the charts. He ranks second in MLB in average exit velocity, third in hard hit percentage and 90th percentile or better in almost every other category, per Statcast. His only obvious weakness is his high walk rate (12.2%), but Scott’s ability to avoid damaging contact has generally allowed him to escape jams whenever men do get on.

A perfect fit

Performance like this obviously isn’t going to come cheap. Spotrac.com has Scott projected at landing a four-year, $60 million deal this offseason, which would rank top-five in MLB among relievers.

That’s a big investment, but it would fall far short of what it would take to land an elite starting pitcher, and it would actually be less than what the Red Sox were paying Jansen annually ($16 million per year). If the Red Sox wanted, they could effectively swap out one closer for another, only in Scott they’d be getting a 30-year-old in the prime of his career rather than a guy who is likely nearing the finish line.

Should the Red Sox sign Scott, he would immediately become the club’s best lefty reliever since Andrew Miller. On top of that, his presence would allow the club to rely less heavily on lefties like Bernardino, Booser and rookie Bailey Horn, all of whom bounced back and forth from Triple-A this past year.

By building up so much bullpen depth, the Red Sox are now in a position where one big addition like Scott really could make all the difference. A group led by Scott, Hendriks, Slaten and Whitlock would have tons of potential, and with a few more high-upside depth guys and a bulk reliever behind them, it’s reasonable to imagine the Red Sox bullpen flipping from a fatal flaw into a genuine area of strength.