It was only a year ago that Chad Green was coming off posting a 4.73 ERA and fighting for the Yankees' fifth starting spot. Likewise, Archie Bradley was on the fringes of the rotation after struggling to a 5.02 ERA for the D-backs a year prior.
Now, heading into the 2018 season, Green and Bradley are ranked among MLB's top relievers.
Green and Bradley (along with other recent examples like Wade Davis, Mike Minor and Brandon Morrow) have showcased the potential for a fringe starting pitcher to dominate in a more limited role. With that in mind, here's a look at four starters who could end up flourishing in a relief role this season.
Danny Salazar
A few pitchers on this list already have a bullpen track record, and that includes Salazar. The Indians right-hander possesses overwhelming stuff; per Statcast™, only D-backs All-Star Robbie Ray missed a higher rate of bats than Salazar among pitchers who induced at least 750 swings last year. Yet Salazar's name has frequented trade rumors this winter, thanks to the Indians' pitching depth and his inconsistent history. The righty logged five different stints on the disabled list over the past two seasons, thanks to shoulder and elbow soreness, and he likely won't be ready for Opening Day.
But Salazar became a weapon for Cleveland last summer in the few instances he pitched in relief. Over four appearances, Salazar struck out seven and walked one in 5 2/3 innings, allowing just one run. And he struck out three Yankees in his lone appearance in the American League Division Series.
As one might expect, Salazar's four-seam fastball velocity jumped from an already-blazing 95.2 mph as a starter to 96.8 mph in relief, per Statcast™. A fastball uptick like that has the potential to set up Salazar's All-World changeup even further, with a relief role carrying the added benefit of putting less strain on his arm.

Kenta Maeda
The proof is already in the pudding with Maeda. The Japanese star has an inside track to a starting spot for the Dodgers, but Los Angeles loves to feature its depth, and it's hard to predict how many starts anyone not named Clayton Kershaw will actually make. Brock Stewart, Thomas Stripling and Walker Buehler, the club's No. 1 prospect per MLB Pipeline, are waiting in the wings and figure to make their share of starts, too.
Maeda made his feelings known last year that he prefers to start, but there's no denying how effective he was as a reliever down the stretch. Maeda's four-seamer ticked up from a 91.9-mph average as a starter to 93.3 mph as a reliever through the postseason, and he subsequently leaned on it way more (33.5 to 39.6 percent), while simplifying to a mostly fastball-slider attack. Right-handed batters hit just .149 (7-for-47) against Maeda when he came out of the bullpen, and his overall 35.5-percent whiff rate ranked among the best pitchers during the postseason.
Brad Peacock
Only nine pitchers induced at least 750 swings and missed more bats than Peacock. Only five faced at least 400 batters and recorded a lower expected weighted on-base average (xwOBA, an advanced Statcast™ metric that calculates how a pitcher should fare based on walks, strikeouts and quality of contact) than Peacock at .262. And yet, the Astros' blockbuster trade for Gerrit Cole makes it likely that one of baseball's top breakout pitchers will begin 2018 outside the rotation.

Peacock's tough luck figures to be Houston's gain. The righty has already proven his versatility, compiling a 1.10 ERA as a reliever last year before he received his first start on May 22. Astros fans won't soon forget Peacock's bullpen cameo in Game 3 of the 2017 World Series, when he twirled 3 2/3 scoreless innings and tied for the longest hitless save in postseason history. Furthermore, Peacock simply dominated lineups the first time through, but increasingly lost effectiveness the more opponents saw him:
First time through the order: .202 wOBA
Second time: .301 wOBA
Third time: .420 wOBA
The Astros, like the Dodgers, have the depth to push a talent like Peacock into a multi-inning relief role and maximize his value there.
Jack Flaherty
Flaherty is a less familiar name than the three listed above, and the 6.33 ERA he posted in six appearances for the Cardinals last September wasn't pretty. Flaherty's inclusion here is based primarily on his tools, specifically his slider. As first pointed out by FanGraphs' Eno Sarris, the movement on Flaherty's slider profiles similarly to the ones thrown by Kershaw and Garrett Richards. Flaherty got his opponents to miss on 25 of their 47 swings against his slider for a 53.2-percent whiff rate that would have ranked among the game's best over even a slightly larger sample.

Flaherty undoubtedly has many steps left to take before becoming a dominant pitcher, but he could be set up for a beneficial situation. The righty appears to be on the outside of the Cardinals' rotation as camp gets started, and he could get plenty of reps in a St. Louis bullpen that is far from established at this point. Opposing hitters would only see Flaherty's sliders a few times per series if he comes out of the bullpen. He could take advantage of the opportunity and lean on his out pitch while developing the rest of his arsenal.