Christian Petersen/Getty Images

The Oakland Raiders aren’t having a flashy start to free agency, but they’ve already managed to add eight new players to the roster. While general manger Reggie McKenzie failed to land a game-changing talent like defensive tackle Ndamukong Suh, he did focus on rebuilding the heart of his defense.

Among the Raiders’ first signings was defensive tackle Dan Williams, formerly of the Arizona Cardinals, who will be the anchor of new head coach Jack Del Rio’s defensive line. Williams will quite literally be the centerpiece of a defense that desperately needs to improve in 2015.

Many believed defensive tackle Terrance Knighton would land in Oakland because he has played for Del Rio for years in Denver and Jacksonville. He seemed perfectly suited to help the Raiders at a position of need, but the team ultimately chose Williams and gave him a lucrative contract.

Williams is such a perfect fit with the Raiders because his impact will go beyond his individual performance. Having Williams will change how the Raiders use some of their other personnel, which essentially makes his signing like signing two or three players.

Unbelievably, the Raiders were actually solid against the run last year on a per-play basis, but they fell behind so much they ended up conceding a lot of yards. Rookie outside linebacker Khalil Mack and rookie defensive tackle Justin Ellis, along with veteran defensive end Justin Tuck, kept things from getting out of hand, but it may have come at the expensive of getting after the quarterback.

Among the problems on defense was that defensive tackle Antonio Smith had to play on running downs and passing downs. Smith ended up playing the fourth-most snaps at the position, which was also the most for any defensive tackle over 30.

Smith hasn’t been particularly good against the run in years, but he has value as a pass-rusher. By signing Williams, the Raiders can shift Smith into more of a specialist role, and he should be more rested and effective that way.

A Balanced Rotation at Defensive Tackle Players Snaps PFF Rush 2014 PFF Run 2014 Antonio Smith 791 (4) +18.3 (3) -20.0 (81) Justin Ellis 642 (18) -8.3 (79) +4.9 (15) Dan Williams 427 (51) +1.3 (33) +11.7 (8) Pro Football Focus

Tuck won’t have to rotate inside on some passing downs with Smith in that role, which frees him up to focus more on getting after the quarterback from the outside where the Raiders still need it. Ellis played more snaps than any other rookie tackle not named Aaron Donald last season, and he struggled when asked to try to get after the quarterback.

Williams adds so much versatility and flexibility to the defensive line that the Raiders can mix and match players depending on the situation. New defensive coordinator Ken Norton Jr. won’t have to ask players to do things they don’t do well.

“I played some three-technique inside, sometimes outside, five-technique depending on who is playing and what front we were in,” Williams told the media via conference call. “I think towards, especially last year, I got to show off a little bit more of my versatility and I just couldn’t be just a regular two-gap nose tackle.”

Williams’ strength is stopping the run. Last season, he was the eighth-best defensive tackle against the run, according to Pro Football Focus, just ahead of Knighton. He finished seventh in their run-stop percentage metric, just behind Suh.

He even held his own against a couple of the best centers in the league in Travis Frederick of the Dallas Cowboys and Rodney Hudson, who was then with the Kansas City Chiefs. The Raiders made Hudson their prize free-agent signing, but even he struggled at times containing Williams.

In this example on 2nd-and-1 against the Chiefs, Williams gets penetration into the backfield and occupies two blockers throughout the play—including Hudson. If not for running back Jamaal Charles’ freaky ability to find creases in the defense and run through them, the Cardinals probably get the stop.

NFL Game Rewind

NFL Game Rewind

Williams draws double teams, redirects offensive lineman and generally frees up his teammates to make plays. It’s not glamorous, but it’s necessary if the Raiders want to be able to stop the run in 2015.

On this play, Williams initiates the contact with Hudson, which actually keeps him from getting to the second level to block linebacker Larry Foote. Since Foote doesn’t have to work through the trash to flow to the play, he’s able to make the tackle after a short gain.

NFL Game Rewind

Williams actually gets illegally chop blocked on the play, as guard Mike McGlynn engaged him below the knee at the same time Hudson was blocking him. The penalty went uncalled, but Foote made the stop after initially using poor tackling form.

NFL Game Rewind

Given how Williams’ plays against the run, new Raiders’ inside linebacker Curtis Lofton has to relish the opportunity to play behind him. Lofton led all inside linebackers with 123 tackles last year according to Pro Football Focus, which isn’t an inflated number like the official NFL statistic.

Lofton graded out as one of the worst against the run, but Del Rio always seems to be able to get his linebackers to perform. One big reason is he finds players like Williams eating space and freeing up his linebacker to make plays.

Of course, in the NFL today, just eating space isn’t enough for a defensive tackle. While useful, the best defensive tackles also have to be able to rush the passer a little bit. What makes Suh such a special player is how well he does both. Donald and Marcell Dareus also did both things well in 2014.

It’s pretty rare to find a defensive tackle who is solid in both areas. Pro Football Focus only graded 12 defensive tackles in the league positively against the run and the pass, and Williams was one of those players.

Williams has also improved his pass rush in each of the past three years. Although he had just one sack in 2015, he added two quarterback hits and 14 hurries on just 187 pass-rush snaps. From a productivity standpoint, that’s not far behind Dareus, who had 10 sacks, two hits and 19 hurries on 410 pass-rush snaps.

The Raiders will likely give Williams more opportunities to rush the quarterback on third down than he received in Arizona. The hope is that he can carry over what he did last year in limited snaps and build upon it.

Williams mentioned in his conference call with local media that the Raiders brought him in to stop the run, “push the pocket a little bit more and try to get pressure on the quarterback also.”

The Raiders were obviously worried about his ability when the Cardinals played the Raiders earlier in the season. Take this early play in the first quarter in which the Raiders committed three players to pass block Williams.

NFL Game Rewind

One of his best performances rushing the passer was against the Dallas Cowboys and Frederick. Williams got his lone sack of the season and nearly had a safety.

NFL Game Rewind

Williams uses his power and leverage to get into the body of offensive linemen and control what they are doing in both the running game and passing game. If he starts to combine his explosive first step and low center of gravity with more than just a bull rush, there’s certainly some upside there.

The Raiders certainly need that from Williams, as they were one of the worst pass-rushing teams in the league last year. The Raiders finished with a sack percentage last season of just 3.9 percent, which was 30th in the league.

Even if he doesn’t improve much in that area, Williams is the new centerpiece for the Raiders from which Del Rio will key much of his defense. The Raiders now have the diversity on the defensive line to have a true rotation, keep everyone fresh and, with some luck and some other pieces brought in, rush the passer.

Unless otherwise noted, all quotes obtained first-hand. All statistics via Pro-Football-Reference or Pro Football Focus (subscription required).