The A’s bullpen had no margin for error. But that turned out to be just fine.

On April 28 at Camden Yards, Oakland starter Paul Blackburn departed after allowing six runs in four innings. With the A’s down 6-4 to the high-powered Orioles, it was up to Oakland’s relief corps to keep the game in hand.

Check.

Four A’s relievers went the rest of the way, keeping the O’s at bay as the A’s rallied for two runs in the top of the ninth for a 7-6 victory and a huge series win. They combined for five scoreless innings with eight strikeouts on the road against one of MLB’s best offenses -- without even having to turn to flamethrowing closer Mason Miller, perhaps the best reliever in the Majors this season.

It’s simply been night and day for the A’s bullpen after a tough 2023 in which they posted a 5.20 ERA, third worst in MLB. Fortunately, given the typical rate of turnover in bullpen personnel, as well as the highly volatile nature of reliever performance, a new year provides a clean slate and an opportunity for rapid improvement.

Sure enough, A’s relievers -- a group comprising converted starters, Rule 5 picks, waiver claims and journeyman veterans -- rank toward the top of MLB in ERA, strikeout rate and Wins Above Replacement this season.

Here’s how Oakland built its 2024 bullpen (largely with unheralded pieces), what’s behind its strong performance and whether there’s more success in store.

All statistics are through Wednesday’s games unless otherwise specified.

A major difference
The 2023 A’s used 41 pitchers -- the most in the Majors -- and few of them saw much success. Only eight of those hurlers finished the year with an ERA below 4, and of those eight, one is retired, two are on Oakland's injured list, two are with Triple-A Las Vegas, and two are with other organizations. (Miller, as usual, is an exception, converting to a full-time relief role and flat-out dominating so far with a 0.98 ERA and 38 strikeouts in 18 1/3 innings.)

A’s relievers gave up 694 earned runs in 2023, the most of any bullpen in the Majors. They converted just 29 of 55 save opportunities (52.7%), the fourth-worst rate in MLB, and were tagged with a league-high 40 losses as the A’s finished with MLB’s worst record at 50-112.

It’s a much different story in 2024, where the A’s rank 11th in ERA (3.49), sixth in reliever strikeout rate (25.2%) and second in FanGraphs WAR (2.1). They’ve only given up 12 homers all year, tied for the fourth-best mark in the Majors. The strong bullpen has helped Oakland beat expectations this season -- the A’s are 19-26 and third in the American League West entering play Thursday after starting out 12-50 in 2023.

“I think that gives the team a lot of confidence just knowing that if we can hand the game over to the bullpen with a lead, you feel pretty good about that game that night,” starting pitcher JP Sears told MLB.com. “It’s definitely something that you didn’t really feel that much of last year, and I feel like we feel that consistently every game this year.”

What can account for such a drastic change so quickly? For one thing, bullpen performance varies considerably from season to season. Based on ERA, there’s almost no correlation between team bullpen results from 2023 to 2024. The same is true when using expected wOBA, a more precise measurement that factors in quality of contact, strikeouts and walks.

It’s not just pure randomness that has made the A’s into one of the league’s better bullpens overnight. Asked the reason for the leap, Sears’ initial answer was “improving on some arms.”

“I think also guys have continued to progress and learn more about what kind of pitcher they are,” he said. “You see guys who have made some adjustments that have been really good for them this year compared to last year.”

‘Growing together’
Who are some of the unsung A’s relievers making the leap this season?

Enough has been written about Miller, who posted a 3.78 ERA in six starts and four relief appearances as a rookie in 2023. But another converted starter, left-hander Kyle Muller, has been a reliable long reliever for the A’s. It was Muller who took the ball from Blackburn in that April game in Baltimore, firing 2 1/3 key relief innings and allowing just one hit. He has a 3.90 ERA in 10 appearances for Oakland, a year after starting on Opening Day and finishing the season with a 7.60 ERA.

Reliever Michael Kelly, an offseason waiver claim from the Guardians, has been even more successful with a 3.00 ERA. He ranks in the 99th percentile in MLB with a 21.9% hard-hit rate.

Right-hander Lucas Erceg, the main setup man for the A’s, has lowered his ERA to 3.18, well below last year’s 4.75 mark. The converted third baseman, acquired for cash from the Brewers on May 17, 2023 -- one year ago Friday -- is in the 99th percentile of MLB with a 98.6 mph average fastball velocity. The second-year pitcher has a 68.8% strikeout rate on his slider (the fourth-best mark on any pitch type in MLB), and his chase and whiff rates are also upper echelon. Pairing with Miller at the back end of the bullpen, Erceg has been quite the find for Oakland.

“To have Mason Miller, to have Lucas Erceg settle in their roles and having success, all of that carries momentum, which I think we’ve seen,” A’s manager Mark Kotsay said.

Another solid find for the A’s so far this year is rookie Mitch Spence, selected from the Yankees with the first pick of the Rule 5 Draft in December. Spence has a 4.26 ERA in 25 1/3 innings, and his Statcast metrics have been impressive so far, including a 3.04 expected ERA.

Spence said that given their relatively humble beginnings, A’s relievers are playing with a chip on their shoulder -- and it’s evident in their strong performance.

“It just kind of goes hand in hand with our team,” he said. “It’s young, and we’re all kind of growing together, so it’s been a fun ride to bounce ideas off each other and have the success together.”

Veteran presence
A pair of established pitchers has gone a long way toward making the A’s bullpen strong in 2024.

On March 24, Oakland acquired right-hander Austin Adams from the Mets. Two days later, the A’s brought in lefty T.J. McFarland from the Dodgers. Both deals cost the A’s only cash, and they netted the club a pair of pitchers with 18 combined MLB seasons.

“Anytime you get some veteran guys down there who bring some experience and a little bit of character -- which I think T.J. and Austin Adams both do – it helps the atmosphere, the culture down there, and it also helps the mentorship,” Kotsay said. “Both those guys have been a part of successful bullpens in the past.”

McFarland -- in his second stint with the A’s after being part of their 2020 bullpen -- has been a victim of some bad luck, as his xERA is just 1.91 compared to an actual ERA of 4.58. Adams, meanwhile, has been dominant, baffling hitters from his sidearm slot and posting a 1.23 ERA in the early going. His 81.1 average exit velocity leads all qualifying pitchers.

“We have some older guys who have been good pieces for us,” Miller said. “T.J. and Austin have been great coming over, doing the roles they’ve been normally doing for their career.”

Adams throws his wipeout slider 82% of the time, the second-highest usage rate of any pitch in MLB. That’s a theme in the A’s bullpen: Entering play Wednesday, Oakland relievers deployed sliders and sweepers 42.3% of the time, the highest rate in the Majors.

Spence -- whose own slider ranks second in MLB in horizontal break above average -- praised the sliders and sweepers thrown by several of his A’s teammates.

“I think everybody down in that bullpen’s got really good weapons, and it’s been fun to watch,” Spence said.

‘You can’t be perfect’
No matter how successful, every bullpen will hit a rough patch eventually. The A’s might have hit theirs.

After seven straight games without giving up a run in relief (26 1/3 scoreless innings in all), the A’s have posted a 5.73 bullpen ERA since May 3, the third-highest in the Majors. Erceg gave up a go-ahead three-run homer to the Rangers’ Corey Seager in the eighth inning of a 4-2 loss on May 6, and the A’s allowed five runs in the eighth and ninth despite a 12-11 win in Game 2 of a doubleheader with Texas on May 8. On Monday, Spence and Easton Lucas gave up five earned runs in the final two innings of a 9-2 loss to the Astros.

Miller said he and his teammates are always prepared to pick up the slack when something goes wrong -- it’s a natural if unfortunate part of every season.

“Your expectation is to be perfect every time you go out, but the reality is you can’t be perfect each time out,” Miller said. “Knowing that you have guys behind you, guys who can pick you up if you do hit a little bit of a bump, I think that’s reassuring.”

The A’s bullpen is actually due for some good fortune. With a .274 xwOBA that ranks first in all of MLB, Oakland has had the unluckiest bullpen in the Majors so far.

But less than two months into the season, that can change as fast as the A’s bullpen went from scoreless to struggling. A’s relievers surely know that -- but all they can do is try to stay in the present, Spence said. For now, he and his teammates will enjoy the success they’ve had so far.

“It’s been a blast,” Spence said. “There’s a bunch of really good guys down there. We keep it light, and we have fun down there. We’ve been on a little bit of a roll, so it’s just been a really good experience.”