The San Francisco Giants’ pitching rotation, barring any injuries, is largely set for 2026. The group will consist of ace Logan Webb, Robbie Ray, Landen Roupp, and two free agent acquisitions in Tyler Mahle and Adrian Houser. 

This group looks to be a strong suit, as all five of these pitchers have shown the ability to produce high-quality innings throughout their Major League Baseball careers. However, the one area that remained largely untouched for the Giants throughout the offseason was the bullpen. 

Both Tyler Rogers and Camilo Doval were moved before the trade deadline last season, leaving Ryan Walker in charge of closing duties. Erik Miller looks to bounce back from last season’s injury trouble, José Buttó was brought over in the Rogers trade, and Spencer Bivens, Tristan Beck, and Matt Gage all remain from last year’s group. 

With those six in the fold, here is a look at three relievers who could play a key role in the Giants’ bullpen success in 2026: Hayden Birdsong, Joel Peguero, and Michael Fulmer.

Three Relievers That Could Play Key Roles in the Giants Bullpen
Hayden Birdsong

Birdsong’s 2025 final numbers weren’t where the 24-year-old or the Giants hoped them to be. The right-hander finished the year with a 4-4 record, an ERA of 4.80, and a 1.49 WHIP across 65.2 innings pitched. Birdsong made his final appearance with the club on July 21, before finishing out the season in AAA with the Sacramento River Cats. 

Birdsong actually started the season as a reliever, pitching out of the bullpen until Jordan Hicks’ struggles forced Birdsong into the rotation on May 20. Before the move to the rotation, Birdsong had a record of 1-0, an ERA of 2.31, and a WHIP of 1.29.

In 23 1/3 innings as a reliever, Birdsong struck out 25 batters and walked only 10, while also holding opposing batters to an average of .230. The outings were generally two-to-three innings, giving the Giants consistent length. While control issues reared their ugly head after the move to the rotation, Birdsong showed he can provide quality innings in a very important role.

Joel Peguero

Last season, Peguero made his MLB debut on Aug. 21 at the age of 28. In 17 games with the club, the right-hander went 3-1 with a 2.42 ERA and 1.03 WHIP. Across 22 1/3 innings, Peguero allowed only 15 hits, holding opposing batters to a .197 average against. 

With a fastball that averages 99.9 MPH, Peguero finds himself in the 99th percentile for average fastball velocity. An uptick in strikeout percentage, which sat at 19.8%, would be the next step in his big league career.

Earlier in spring training, Peguero suffered a grade two hamstring strain, leaving his Opening Day availability in question. Having yet to make an appearance in camp, the most likely scenario is that Peguero opens the season on the injured list before working his way back onto the Giants roster due to the upside showcased last season.

Michael Fulmer

Signed to a Minor League deal in February, Fulmer has been a bright spot with the Giants in spring training. Through five appearances, Fulmer has only allowed one run, via a solo home run, held opposing hitters to a batting average of 0.53, and has struck out nine batters in six innings. 

The former 2016 American League Rookie of the Year appeared in only three games last season with the Boston Red Sox and Chicago Cubs, before making stops in AAA with both the Kansas City Royals and Seattle Mariners organizations. 

The right-hander finished the season strong in Tacoma with the Rainiers, pitching in 12 games, recording one save, an ERA of 0.75, and a WHIP of 1.00. Through the 12 innings, opposing batters could only muster a .163 average, while also striking out 18 batters. If Fulmer can continue to post strong numbers this spring, he is going to make a case to be a factor in the Giants’ bullpen in 2026.

 

Main Photo Credit: Rick Scuteri-Imagn Images