The move coincided with the news that right-hander Gary Glover had been placed on the 15-day disabled list with right shoulder tendinitis retroactive to April 26 and that Al Reyes [right shoulder impingement] will remain on the disabled list longer than expected.
"It was a tough decision," Maddon said. "I told [Hammel] to keep working, keep battling. It was just a tough decision we have to make right now."
In addition, outfielder Justin Ruggiano was recalled from Triple-A Durham for Friday and Saturday's games, and the plan is to send him back to Durham on Sunday when Scott Kazmir is activated prior to his start against the Red Sox Sunday.
"[I'm} disappointed, but it's my job to help the team," Hammel said. "If this is the right move for the team, I'll gladly do it, you know -- just make the adjustments I needed to make, get ready to pitch every day. That's what I needed to focus on."
Hammel, who is 2-2 with a 4.88 ERA in five starts this season, took the loss Tuesday night in Baltimore when he allowed three earned runs on six hits and four walks in 2 2/3 innings. Meanwhile, the other starters in the rotation -- James Shields, Matt Garza, Andy Sonnanstine and Edwin Jackson -- all had decent starts.
"I asked Joe [if the bad start influenced the decision] and he said it was something that had to happen no matter what," Hammel said. "I kind of saw it coming. The timing of it, for me, wasn't the best. But I've still got a job to do -- get guys out."
Aside from his disappointment, Hammel is pleased to continue wearing a Rays uniform.
"The way to look at it is this team is playing really well right now," Hammel said. "And when you're winning ballgames, to move a successful starter out of the rotation just to bring back another one -- it's a good problem to have. We're going to keep going. I'm going to do my job in the 'pen and we're going to see how it goes. ... I'm happy to still be a part of this team."
Glover said his shoulder got to the point where he was having a tough time "bouncing back on a daily basis."
"We don't want to put any extra stress on the guys down there doing their part for the team," Glover said. "Hopefully, it's just something where I need a little extra time off to nip it in the bud."
Maddon said Reyes just wasn't ready to return yet, and given the team's crowded pitching situation, there was no reason to rush him back when he might not be totally healthy.
With Hammel moving to the bullpen, he'll likely handle the long-relief duties while J.P. Howell, who was handling long relief, will move to shorter inning situations.
Hammel made his first relief appearance of the season on Friday night when he entered the game in the seventh and retired the Red Sox in order. He then surrendered one run on three hits in the eighth.
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.