Kelly signs seven-year, $50.5 million contract with Raiders

The Oakland Raiders stepped forward Thursday on the eve of free agency and signed Tommy Kelly to the largest contract ever given to a defensive tackle.

Kelly, a defensive end scheduled to move to defensive tackle this season, signed a seven-year, $50.5 million contract Thursday that has $18.125 million in guarantees. In the first three years of the deal, he will make $25.125 million.

The Raiders' plan is for the 300-pound Kelly to replace the retiring Warren Sapp as the three-technique defensive tackle in the Raiders' 4-3 defense. The move is similar to the one made last year by the Detroit Lions' Cory Redding, a franchise player who signed a seven-year, $47.5 million deal last summer, the highest among defensive tackles at the time.

Like Kelly, Redding was an effective run-stopping end with some pass-rush ability so the Lions believed he could move to tackle, work next to Shaun Rogers and create a solid 1-2 interior defensive tackle punch. The Raiders believe Kelly can emerge as one of the league's best interior defenders.

Kelly gained the confidence of Raiders coaches by averaging five tackles a game as a starter at defensive end. He's had 13 career sacks, and the Raiders believe he can be a pass-rushing force at defensive tackle because of his quickness.

First, though, Kelly has to get healthy. He's coming off a torn ACL that limited him to seven games last year. He had 30 tackles and a sack in those games. Kelly was going to be a highly coveted defender in free agency because he could play defensive tackle in a 4-3 or defensive end in a 3-4.

He came to the Raiders in 2004 as an undrafted free agent out of Mississippi State.

John Clayton is a senior writer for ESPN.com.