Mason Miller has been the breakout bullpen star of 2024. The converted starter -- who began his college career at Division III Waynesburg University in Pennsylvania -- has become a lights-out closer for the A’s, routinely reaching into the triple digits and blowing away practically everyone with his electric fastball.

But Miller isn’t the only reliever success story of the season. While established names like Emmanuel Clase, Clay Holmes and Ryan Helsley have seen continued success in 2024, plenty of pitchers have come from more humble origins to excel in the early going.

Here are six bullpen breakouts you should know about.

All statistics are entering play Friday.

Yimi García, Blue Jays
Now with his fourth team, the 10-year veteran reliever is in the midst of a career-best season. García has been a lockdown arm for the Blue Jays, posting a 0.47 ERA and 24 strikeouts in his 19 innings of work in 2024. His .081 opponents’ batting average leads all pitchers with 10-plus innings in 2024, and his .137 xBA is third in MLB. Hitters are chasing 38.5% of the time against García, one of the best rates in the league.

García’s success is a bit of a surprise for a 33-year-old who throws two of his six pitches with well-below-average vertical movement. But García still averages 96.7 mph and has reached as high as 99.8 mph on his four-seam fastball, giving him the velocity to elude bats at an above-average level. He missed nearly two weeks in late April and early May with a back issue but has returned to fortify Toronto’s bullpen.

Matt Strahm, Phillies
Excellent strikeout and walk rates have made Strahm an excellent option in multiple roles out of the Phillies’ bullpen. The lefty has struck out 30 batters in 20 2/3 innings while allowing just two free passes, and he’s given up only two earned runs all season for a 0.87 ERA. Strahm, who drew some starts early last season for Philadelphia, has been effective while appearing anywhere from the fourth to the eighth inning.

The southpaw uses his four-seam fastball 55.9% of the time and has allowed just a .130 batting average and .217 slugging percentage against the pitch, thanks to elite horizontal movement. He’s been a key part of a Phillies pitching staff with the third-best ERA in MLB. (Strahm’s bullpen teammate Jeff Hoffman, who has a 1.25 ERA so far, just missed the cut for this list.)

Justin Martinez, D-backs
Martinez has made a name for himself in his rookie season thanks to a fastball that nearly rivals Miller’s. Martinez is averaging 100.1 mph between his sinker and four-seamer, and he has also shown high whiff rates on his slider (46.9%) and splitter (52.0%). It’s added up to a 0.64 ERA in 14 innings for the 22-year-old, a year after he put up a 12.60 ERA in 10 innings in his brief 2023 debut.

Martinez has yet to allow a barrel this season and is limiting opposing hitters to an 85.5 mph average exit velocity. A high walk rate of 16.9% is a red flag for the young right-hander, but it should come down with time as the rookie learns to control his electric fastball. For now, Martinez has been practically unhittable and a key asset for Arizona.

Bryan Hudson, Brewers
Hudson, who made his debut for the Dodgers in 2023, was traded to Milwaukee on Jan. 3 for Minor Leaguer Justin Chambers. He’s been an excellent pickup for the Brewers so far, owning a minuscule 0.68 ERA in 26 1/3 innings and striking out 31. Hudson has gone two or more innings in seven of his 18 appearances, including a three-inning stint to get the win in his first outing on March 31 in New York.

Hudson’s Statcast metrics, including a 2.02 xERA (97th percentile) and .178 xBA (98th) back up his stellar performance. The 27-year-old lefty also gets 7.4 feet of average release extension, meaning his release point is closer to home plate than almost all other hurlers. With Brewers closer Devin Williams still on the shelf, Hudson has been crucial for Milwaukee’s relief corps.

Cade Smith, Guardians
Pretty much any Guardians reliever could have made this list, with Nick Sandlin, Hunter Gaddis and Tim Herrin also being strong candidates. But let’s go with Smith, the rookie from Canada, who has been excellent in his debut season. The 25-year-old has posted a 2.01 ERA with 32 strikeouts in 22 1/3 innings as part of a Cleveland bullpen that leads MLB with a 2.59 ERA.

Smith’s performance has been backed up by most Statcast metrics, including a 2.52 xERA (93nd percentile) and .201 xBA. Thanks to 7.5 feet of extension (tied for third-most in MLB), Smith garners enough deception to strike out an elite 36% of batters. He has allowed just a .145 batting average on his four-seamer and .200 on his splitter this season, holding hitters to a .173/.247/.272 slash line in 2024.

Mark Leiter Jr., Cubs
Leiter was a successful reliever for the Cubs in 2022 and 2023 but has taken a major step forward early in 2024. The right-hander has a 0.90 ERA and 26 strikeouts in 20 innings of work, pitching primarily in the seventh and eighth innings for Chicago. Leiter, who debuted with the Phillies in 2017 but did not pitch in the Majors from 2019 to 2021, has made quite a career resurgence.

Leiter's early breakout has been fueled by missing bats at a high level. The righty's 34.6% chase rate ranks in the 91st percentile, while his 34.5% whiff rate ranks in the 94th percentile. Leiter's splitter has been dominant: Hitters are 1-for-33 against the offering with a massive 61.8% whiff rate against it. Leiter throws the splitter 33.9% of the time, but 21 of his 26 K's have come on the hard-to-hit pitch.