According to Ian Rapoport of NFL Network, the Patriots signed Kelly to a two-year deal on Monday:
Patriots head coach Bill Belichick has spoken highly of Kelly in the past—specifically, before the 2005 opener, when he regarded Kelly's ability to line up at different spots as a positive that allows a team to line him up where he'll create the best mismatches (via ESPN):
Kelly plays everywhere. He's a little bit like Howie Long in that Howie Long was a guy that they would move along on the front. They would take Howie and mismatch him against whoever they thought the other team's worst lineman was. There is a little bit of that with Tommy Kelly, too, find a guy that they want to go after and stick him there because he does have the flexibility to play outside and inside. He can pretty much play across the board. He can do everything. Play the run, rush the passer, he's good in pursuit. He's a very physical player.
Kelly played 776 snaps for the Raiders in 2012, the second-most for any defensive linemen on the roster last year. The Raiders defense has been ever-changing between the 3-4 and 4-3 fronts over the years, and although that's likely been a source of frustration for most of the players constantly having to learn new schemes, it has only helped make Kelly a highly scheme-versatile lineman.
The Patriots have a need for improvement in their interior pass rush, and Kelly was providing a good push up the middle as recently as 2011. He had 46 hurries, 17 hits and 15 sacks (half-sacks counted as full sacks) on 968 pass-rush attempts from 2010 to 2011. That means he was generating pressure 12.4 percent of the time he rushed the passer in that span.
He wasn't nearly that disruptive in 2012, logging 12 hurries, six hits and one sack on 416 pass-rush attempts (4.6 percent). When I asked colleague Christopher Hansen why that was the case, he explained it may have been due in part to how he was used, but also could have simply been a product of being the most game-planned player on a bad defense:
Kelly was asked to defend the run a lot more in 2012 than he has in previous years which hurt his production. Offenses didn't have to worry about the outside speed rush from the Raiders in 2012 either, which made things more difficult for him. Kelly was at his best when Seymour was at his best because he rarely had to worry about a double-team. He's still a good player and is at his best when he can just go after the quarterback. He seems like a very good fit next to Wilfork.
The Patriots have targeted other Raiders castoffs along the defensive line with some success and some failure.
Defensive end Derrick Burgess was a notable failed attempt at striking gold with a formerly productive player off the edge. Defensive tackle Gerard Warren was a nice rotational piece in 2010 and 2011, and Kelly figures to fill that same role as a three-technique defensive end in three-man fronts or as a conventional defensive tackle in four-man fronts.
He will be part of a large battle for playing time on the inside—a battle that already consists of defensive tackles Kyle Love, Myron Pryor, Brandon Deaderick and recently added defensive lineman Armond Armstead.
Kelly's presence adds a seasoned veteran to that competition, which rounds out the lineup and increases the likelihood that the Patriots will get more production from their interior defensive linemen than they got last year.
Erik Frenz is also a Patriots/AFC East writer for Boston.com. Follow Erik on Twitter and "like" the AFC East blog on Facebook to keep up with all the updates. Unless otherwise noted, all stats obtained from ProFootballFocus.com, and all quotes obtained firsthand or via team press releases.