This year's free-agent market for relievers was long known to be a weak one, and teams, knowing that, went all out to retain their best free-agent arms before they ever reached the market -- like Edwin Díaz, Robert Suarez and Rafael Montero. What’s left, then, is a collection of older pitchers coming off mostly uncertain seasons. You might have to pay more than you would expect for one of the older, still-effective names (like Kenley Jansen, 35, or Adam Ottavino, 37), or gamble on the name value of the inconsistent Craig Kimbrel (35), or hope that Taylor Rogers (soon to be 32) is a lot more like he was before 2022 than in 2022, or work your way down from there.

All of which means that teams will look to the trade market or, in some cases, bet they can bring out the best in some lower-tier arms who haven’t exactly had long track records of success. It’s that group that we’re interested in now, the flamed-out long-ago top prospects or the anonymous middle relievers, the non-closers who don’t make All-Star teams. Each year, we see a handful of those players land somewhere and end up offering big returns. Here are four of the most interesting available this winter.

Shelby Miller, RHP

Yes, that Shelby Miller, the one chosen six picks before Mike Trout in the first round of the 2009 Draft. Miller looked like a breakout young Cardinals ace (3.33 ERA in 69 games through age 23) before he was flipped to Atlanta for Jason Heyward in 2015. Then, after one successful season as a Brave (3.02 ERA in 205 1/3 innings), he was sent to Arizona in one of the all-time trade heists, a deal that sent No. 1 overall pick Dansby Swanson and future three-time Gold Glover Ender Inciarte back to Atlanta.

Miller was rarely healthy and never effective as a D-back, posting a 6.35 ERA across parts of three seasons, and he was let go after 2018. In the five seasons since, he’s cycled through the organizations of the Rangers, Brewers, Cubs, Pirates, Yankees and Giants, putting up an 8.48 ERA in 36 scattered Major League games. Now that Miller is 32 years old, nearly seven years removed from his last big league success, you might have written him off. You might have forgotten about him entirely -- and the five runs he allowed in four late-season games for San Francisco (6.43 ERA) probably aren’t doing much to change your mind.

Generally, that kind of profile leads to another non-roster invite, if even that. But the interest in Miller was clearly high, because The Athletic's Ken Rosenthal reported on Tuesday that the Dodgers were in agreement with Miller on a deal, pending a physical.

Though the Dodgers were probably not putting too much stock into seven late-season innings, it was likely also hard to ignore that Miller faced 30 hitters and struck out 14 of them, a 48% rate. It’s a tiny sample, sure. It’s also not something you do by accident.

That said, teams that were interested in Miller probably wanted to see some reason behind that, some change that indicates he’s doing something differently than before. Take a look at his pitch usage over the years, and take a look at the yellow line, the slider. Anything stand out?

Right. There's that slider, more than half the time.

For years, Miller was an 80% fastball pitcher, but in his brief 2022 look, he was down to a mere 45% heaters, because the slider was his primary offering. When he arrived in Cubs camp in 2021, it was with what was then described as a brand-new slider -- “I've never had something that was kind of nasty that people swung over the top of,” he said -- and then he reportedly learned a new grip on it as a Yankees Minor Leaguer in 2022. None of that overshadows more than a half-decade in the wilderness, of course. But it does explain why teams like the Dodgers were interested in this seemingly new version of Shelby Miller.

Carlos Estévez, RHP

Estévez has thrown in 321 games dating back to 2016, all for one team, and you’d still be forgiven if you don’t know which team that was. (It was the Rockies.) As is almost always the case, it’s extremely difficult to evaluate pitchers who have had to suffer through Coors Field that long, and you’ll be absolutely shocked to know that Estévez has a 5.57 career ERA at home and a 3.51 career ERA on the road. Still, he's an extremely interesting possibility due to his relative anonymity, big arm and the reputation of the Rockies as a team that’s not exactly on the level of the Dodgers, Rays or Astros in terms of pitcher development.

Let’s start with that arm, because the velocity is for real. Estévez has averaged 97-98 mph on his fastball for years; in 2022, his 97.5 mph heat was in the 95th percentile for velocity. Since his 2016 debut, only three relievers have thrown more four-seamers 95 mph or harder: Aroldis Chapman, Craig Kimbrel and Díaz.

It’s not hard to see a progressive team seeing that velocity and those Coors splits and salivating at what they might be able to help him become -- a team like, for example, the Dodgers, who took his longtime teammate Yency Almonte (6.46 home ERA as a Rockie, 3.74 road), helped him lean more on his sinker and slider and were rewarded with one of 2022’s more effective relievers. It’s easy to see Estévez being asked to throw that four-seamer less than the 71% of the time he just did. Take the high-end velo, toss in a few more breakers, get away from altitude and suddenly you might have something special.

It’s not always that simple. But, also, sometimes it is. Either way, it’s worth pointing out that Ken Rosenthal has reported that teams see Estévez as “a potential high-leverage piece … [or] a potential closer.” It’s not hard to see why.

Matt Moore, LHP

Moore’s path is something like Miller’s, except without the earth-shattering trade. A decade ago, Moore was a high-quality starter for some high-quality Rays teams, but Tommy John surgery ruined his 2014-15 seasons, and a 2016 trade to the Giants brought early returns -- a near no-hitter in August, then eight shutout innings in the NLDS against the eventual champion Cubs in October -- before it all fell apart. He posted a 5.99 ERA from 2017-18, blew out his knee in his second start of 2019, went to Japan for 2020, then had a 6.29 ERA when he wasn’t dealing with back trouble for the Phillies in 2021.

It was a journey, is the point, and it left him having to sign a low-cost non-roster deal with Texas in 2022, when he didn't even make the Opening Day roster. After a pair of appearances with Triple-A Round Rock, Moore was called up, and … he was great. His career strikeout rate through 2021 was 21%, but in 2022, it jumped to 27%. He still walked too many, but where he’d once allowed terribly high hard-hit rates -- he was in the 4th percentile in 2017 and 2nd percentile in 2018 -- he was in the 93rd percentile in 2022.

Basically, “strike out more and allow less loud contact” is a nice recipe for success, and that’s how you achieve a 1.95 ERA. But, as with Miller, the question is how, and as with Miller, it starts with “throw a bendy pitch a whole lot more,” while also losing his cut fastball. This time, look at the blue line, the curveball.

Or, perhaps: Improve that bendy pitch first. Just look what MLB.com’s Kennedi Landry wrote in April:

“Moore credits co-pitching coaches Doug Mathis and Brendan Sagara for helping him tweak the grip on his curveball, which he threw 12 times (40 percent) in his [April 27] outing against the Astros,” wrote Landry, “and just slightly adjusting the grip on his four-seamer.”

Compared to 2021, Moore’s curveball went from two inches of drop below average to one inch above average, while also adding 3 mph of velocity; his fastball also gained rise while adding velocity. Like Miller, it’s not that important how many places he had to stop to get here, nor what his career numbers might say. It matters what he’s ready to do in 2023, not what he did in 2013.

Chris Martin, RHP

Martin, in our view, shouldn’t be “under the radar,” for reasons we’ll explain in a moment. But when he signed with the Cubs last year, it was for a mere $2.5 million. When he was traded to the Dodgers in July, the cost was utility player Zach McKinstry, who has a career 78 OPS+. And when FanGraphs crowdsourced contract estimates for its Top 50 free agents this offseason, he didn’t even make the cut. He's just routinely not valued highly.

Martin is 36 years old, which certainly explains some of the hesitancy here, and we don’t mean to overstate his candidacy. But all Martin does, all he’s done for years, is collect strikeouts and avoid walks. With the Dodgers, he whiffed 34 while walking just one; over the last three seasons, he’s struck out nearly 10 times (127 whiffs) as many as he’s walked (14). Martin might have only 251 career Major League innings after all this time, but he’s also got the best strikeout-to-walk ratio in integrated AL/NL history. The. Best.

He’s also been excellent in the postseason -- a .592 opponents' OPS and 1.88 ERA in 14 1/3 innings -- if that helps his case, but mostly, despite the fact he’s not getting younger, there’s little evidence that the cliff is nearing; in 2022, Martin’s four-seamer averaged 95.3 mph.

If anything, there’s evidence that there may still be more in there, because Martin was outstanding after the trade to Los Angeles (1.46 ERA), and it didn’t happen by accident. As a Dodger, Martin prioritized his four-seamer and cutter at the expense of his relatively ineffective slider; he finished the year with 13 straight scoreless appearances. At his age, he’s unlikely to get more than another one-year contract, which means there’s not a team in the Majors that shouldn’t have room for him.