Assessing the risk in signing Andrew Miller or Zach Britton

If you’ve paid even a marginal amount of attention to the Red Sox in the offseason, you know that the most likely spot on the roster the Red Sox will look to improve this winter is going to be the bullpen. Although, in this writer’s opinion, the unit was never quite as bad as the general consensus seemed to agree it was, it was always the portion of the roster that had the most room for improvement. Then, after the season, they lost two of their key arms to free agency in Craig Kimbrel and Joe Kelly. Even with those two there was clear room for improvement in relief, and that’s even more clear without those two. So, naturally, the Red Sox have been connected to the top bullpen arms available on the market, including Kimbrel and Kelly. A couple of those relievers are lefties, which the Red Sox lack, but with each carrying some serious question marks it’s unclear if Boston should aggressively pursue both or either.

Earlier in the offseason we talked about the possibility of the team signing a left-handed reliever, and the conclusion was that while it would be nice if they grabbed a southpaw acquiring talent regardless of handedness is what matters the most at this point. That being said, at least in terms of name value Zach Britton and Andrew Miller are two of the biggest names available in free agency this year, so they are both natural targets for the Red Sox. It also hopes that the Red Sox are very familiar with both lefties. However, there is some question about whether their real-world value matches the name value. Let’s take a quick look at each and see whether the risk is worth it for either southpaw.

We’ll start with Zach Britton, who the Red Sox know quite well considering he has spent his entire career to this point in the American League East. Most of that time was, of course, spent with the Orioles before he was traded to the Yankees this past summer. According to the New York Post, Boston is seen as a real possibility for both Britton and former Yankee David Robertson. We talked about Robertson a few weeks ago and determined he’d be a strong fit. Britton carries a different kind of risk, though.

Britton was once one of the very best relievers in all of baseball, and had an argument for being the best, but the last couple of seasons have been a disappointment. He’s battled injury issues in both 2017 and 2018 — the first season was marred by a forearm injury and this past year was delayed because of an Achilles injury suffered during the previous winter — and his performance suffered in each season as well. Although his ERA’s look good in both 2017 and 2018, his peripherals don’t tell the same story. Both his strikeout and walk rates got significantly worse compared to his spectacular 2015 and 2016 seasons, and as a result he posted DRAs that 26 and 56 percent worse than the league-average pitcher.

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The question becomes whether or not you believe A) his injuries were the cause of his issues and B) a fully healthy offseason will remedy those issues. There is certainly a fair chance this can happen, particularly because his stuff doesn’t appear to be the major issue here. Despite his declining strikeout rate, he still appeared to have similar stuff to his peak. In 2018, according to Baseball Prospectus’ plate discipline numbers, his swinging strike rate was still up at 32 percent. For context, that put him in the same range as guys like Corey Knebel, A.J. Minter, Chris Devenski and Brad Hand. The issue was that his command just couldn’t prop up his strikeout numbers. He was too easy to lay off, and even with swinging strikes the swings just didn’t come enough.

His control is harder to predict than his stuff, but I’m not as confident in it. It’s hard for it to get worse, to be fair, but Britton’s zone rate has consistently been on the way down over his entire time as a reliever. It is certainly fair to wonder if concerns about his ankle messed with his delivery in 2018 and if a healthy offseason could help get his mechanics back on track, but I’m not sure I’d pay a premium for a pitcher trying to regain that kind of form as a 31-year-old.

Meanwhile, Andrew Miller is obviously familiar to the organization since the Red Sox were the ones who helped the big lefty blossom into one of the best relievers in baseball. That’s exactly what Miller has been for the better part of this decade, but he started to show signs of decline in 2018. For one thing, the injury bug caught up to him just as it has with Britton for a few years running. After a long run as one of the most durable top relievers in the game, regularly tossing 60-70 innings before taking on even more work in the postseason, the southpaw only pitched 34 innings in 2018 due to shoulder, knee and hamstring injuries that affected him all season.

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In terms of numbers, Miller was kind of the opposite of Britton in that his ERA didn’t look great but the more advanced numbers made a positive case for him improving in 2018. Although the three-year Indians star posted a 4.24 ERA in 2018, he backed that up with a 3.54 FIP and a 3.08 DRA. That would indicate he could be a buy-low, right? Well, for one thing, teams aren’t dumb enough to pay contracts based on a single-season, 34-inning sample of ERA. Plus, even if the peripherals are fine they also show signs of decline. His strikeout rate, home run rate and walk rate all got worse, and his plate discipline numbers also dropped across the board. Miller also saw his average fastball velocity drop to under 94 mph for the first time as a reliever.

The obvious counter to all that is the injuries, but that’s also a major reason for concern. Shoulder injuries in particular are obviously terrifying for a pitcher, particularly one who is going to turn 34 early in the 2019 season. We saw him try and fail to come back strong from the injury multiple times this past year, and it’s reasonable to think that could continue to happen in the future. If completely healthy, I don’t doubt that Miller’s stuff is still good enough to put up strong numbers, but he’s an aging pitcher with a lot of mileage on his arm who is coming off a year marred by a trio of injuries.

Ultimately, while these two are connected for obvious reasons based on their past, I’m much more comfortable with Miller than with Britton. Miller has been better recently, has better underlying numbers as well as a history in Boston. Looking at predictions for free agents, it’s also pretty much agreed that Britton will get a three-year deal. The risk is big enough with both of these pitchers, and the market for late-inning relievers is deep enough that I’d be hesitant to give either one more than a one-year deal with some sort of option for a second year. Miller seems most likely to get this kind of deal, but if both are commanding more than that — and I suspect they will — I’d move on to the right-handed portion of the market and maybe look at lower-end lefties that can be had for cheap.