LOS ANGELES -- With right-hander Jason Marquis activated from the disabled list and pitching against the Dodgers on Sunday afternoon, the Nationals moved right-hander Craig Stammen to the bullpen and placed left-hander Ross Detwiler on the 15-day disabled list retroactive to Aug. 6 with a right hip strain.

The Nationals thought about moving Stammen to the bullpen as far back as last offseason. However, he started the season in the rotation before being sent down to Triple-A Syracuse in early June. Stammen returned to the big leagues less than a month later and was 2-1 with a 2.38 ERA after the All-Star break. He'll be a long reliever.

"It's a different role, different job," Stammen said. "I'll go out there and pitch the best that I can. Second half of the season, I pitched much better. The first half was a little bit of a learning experience. I was coming off elbow surgery and all that.

"I was a little disappointed not to get the start because I was on a little bit of a roll. It's not a big deal. I'm going to the bullpen; it's another challenge for me. It's another way I could help the team. I look forward to it."

Manager Jim Riggleman said Stammen became a reliever because the team has too many starters.

"The people we have coming from injury are starters, whether it's Marquis or Stephen Strasburg," Riggleman said. "Down the road, we'll have Yunesky Maya. These guys are all starters, so we can't have seven or eight starters. To be on the ballclub, Stammen has to be in the bullpen."

As for Detwiler, he will have an MRI on Monday to see what is wrong with his hip, the same hip that was operated on during Spring Training. Detwiler started feeling pain after his last start against the D-backs on Thursday. He was unable to have a bullpen session Saturday and the injury didn't get any better Sunday.

"It doesn't feel very good," Detwiler said. "I'm going to get an MRI tomorrow. I hope to find out more. We are hoping it's scar tissue and we take it day-by-day."

Detwiler missed the first half of this season after having surgery to repair a labral tear in his right hip.

With Stammen and Detwiler out of the rotation, it means right-hander Livan Hernandez will pitch Thursday against the Marlins and John Lannan will be on the mound Friday against the D-backs.

Kennedy gives his side of errant throw

LOS ANGELES -- In the fourth inning in the Nationals' 3-2 loss on Saturday, the Dodgers had the bases loaded with one out. Matt Kemp hit a ball that looked like a grand slam over the right-field fence, but Mike Morse jumped and made a sensational catch.

Ryan Theriot scored easily on the sacrifice fly, while Ethier scored the tying run on a throwing error by second baseman Adam Kennedy, who thought he could double up James Loney at first base. Unfortunately, no one was covering the bag. Kennedy saw three Dodgers near the first-base bag and thought someone was covering first base.

However, first baseman Adam Dunn was on the infield grass looking to cut off the throw home from Kennedy.

Kennedy said he saw Loney on second base and his instincts were to throw to first base.

"Before Mike made the catch, I looked over my shoulder and saw Loney was still at second base," Kennedy said. "I knew we had a play at first base. There were three people over there and I figured Dunn was one of them."