Long known as one of the more respectable batters among major league hurlers, the 24-year-old Bumgarner went deep off of Arizona Diamondbacks reliever Matt Stites in the sixth inning of Sunday's eventual 8-4 Giants win.
The home run, which was Bumgarner's third of the season and fifth of his career, pushed his season-long slash line to an impressive .275/.302/.550. He previously hit a grand slam on April 11 against the Colorado Rockies and now has 12 RBI through just 40 at-bats this season.
Previously, the only pitcher to hit multiple grand slams in a season was Tony Cloninger, who smacked two for the Braves in their first season in Atlanta, back in 1966. Though his career wasn't remarkable from either a pitching or hitting perspective, Cloninger walloped five of his 11 career home runs during that 1966 campaign, one year after posting a 24-win season.
Bumgarner earned a second slice of baseball history Sunday, as he and star Giants catcher Buster Posey became the first starting pitcher-starting catcher duo to both hit grand slams in the same game, per MLB Stat of the Day.
Posey's third-inning slam accounted for San Francisco's other four runs, as the batterymates knocked in all eight of their team's runs.