The injury required the A's place Pomeranz on the 15-day disabled list Tuesday.
"I just let my emotions take over me, and I did something stupid," Pomeranz told reporters. "It sucks. Obviously, I didn't mean for it to happen. It sucks because I want to play, I want to pitch. I'm trying to win games and help the team out. Obviously, I'm not helping the team out when I do something stupid like that."
Pomeranz (5-4) struggled in his shortest outing since joining the A's rotation in early May. He allowed eight hits and eight runs -- seven earned -- with two walks and four strikeouts.
"Hopefully, I'll be back as soon as possible," Pomeranz said. "This is the first time I've broken a bone, though, so I don't know.
"I play it over and over in my head -- wish I hadn't done it. I was walking up to the clubhouse and was just mad."
Oakland filled Pomeranz's roster spot by calling up right-handed reliever Evan Scribner from Triple-A.
Information from The Associated Press was used in this report.