Marshall never played safety in his life until 2011, when he spent a season at the position with the Arizona Cardinals.
During the Chargers' second preseason game, safety Jahleel Addae injured his hamstring, leaving an opening at the position.
Marshall, 29, made his San Diego debut at safety on Sunday, and the veteran says he has no problems with the change.
"That's part of being a pro," he said. "Whether you want to or not, if they asked you to do it and you can do it and it's going to help the team, you need to do it ... I didn't have a problem with going back there."
Marshall had two sacks, three interceptions and 78 tackles as a safety with the Cardinals in 2011.
- Molly Geary