Spencer was released last week after eight seasons with the San Francisco 49ers and quickly found a new home across the bay with the Raiders, who were looking to bolster their depleted secondary.
"Shawntae looked at the opportunities and options and thought the Oakland Raiders were the best situation for him," said his agent, Peter Schaffer. "He was very impressed with the coaching staff and is very excited to be an Oakland Raider."
Spencer is already familiar with Oakland's new defensive coordinator, Jason Tarver, who was a defensive assistant for most of Spencer's tenure with the 49ers.
Spencer started 72 games his first seven years for San Francisco, including all 32 in 2009-10. But he lost his job in training camp last year and spent most of his final season with the 49ers as a reserve.
Spencer, a second-round pick out of Pittsburgh in 2004, has 11 interceptions and 58 passes defensed in his career. His most productive season came in 2005 when he had four interceptions. He had three interceptions in 2010 but struggled at times in coverage that season. He allowed 48 catches on 75 passes his direction for 631 yards and four touchdowns that season, according to STATS LLC.
His role with the Raiders is not immediately clear. Oakland cut its two starting cornerbacks from last season in Stanford Routt and Chris Johnson and signed free agent Ron Bartell last week. The only other cornerbacks on the Raiders roster currently are Chimdi Chekwa and DeMarcus Van Dyke, who played sparingly as rookies last season.
Carlisle, who was released last week by Oakland in a cost-cutting move, started 79 of 80 games at right guard after joining the Raiders in 2007. Oakland signed guard Mike Brisiel to a four-year deal worth almost $20 million last week. The Raiders could move last year's other guard, Stefen Wisniewski, to center to replace free agent Samson Satele.