The Oakland Raiders returned two defensive starters in 2013, and one of those starters—safety Tyvon Branch—is out with an injury. The other starter—Lamarr Houston—has switched from left defensive end to right defensive end.

Considering that the Raiders basically picked up an entirely new defense in free agency, it was hard to know what to expect from the unit. The results have been positive so far, and the Raiders have allowed just 22 points per game, tied with the Pittsburgh Steelers—their opponent Sunday—for 13th in the league in scoring defense.

Can a ragtag group of veteran defensive players and a couple rookies legitimately become a top-10 defense? It might seem far-fetched, but they can if the players continue to buy into what defensive coordinator Jason Tarver and head coach Dennis Allen are selling.

The Raiders have already demonstrated improvement, having only allowed 17 points per game for the last three games if you subtract interceptions returned against the offense for touchdowns against Washington and Kansas City. Last season, the Raiders were the 28th scoring defense after allowing 27.7 points per game.

One of the ways the Raiders have been successful is by creating confusion. The Raiders have managed to make things look complicated for the offense, frustrating quarterbacks like Robert Griffin III, Philip Rivers and Alex Smith in three consecutive weeks.

“They did a great job mixing it up,” said Smith after the Chiefs beat the Raiders 24-17 in Week 6 via ESPN.com.

"I felt like we never could get a read on it, on what they were doing … they just kept rolling through the calls and mixing it. They did a great job. They caught us off guard a few times. They caught me off guard.”

The Raiders don't have a truly elite pass-rusher on the team, and as a result, they blitz more than almost any other team. Sending five, six and seven guys is common for the Raiders, but they have somehow avoided becoming predictable.

One of the keys to Oakland's success has been the design of the defense. Defensive coordinator Jason Tarver has a master's degree in biochemistry and molecular biology, but he hasn't given his defense a crash course in complicated.

Instead, Tarver categorizes plays and makes it simple for his defense. The idea is to have something that looks complicated to the offense but is easy for the defense to understand. From there, it's up to the players to make plays.

“We can make the look look totally different by only switching two or three guys and what they do,’ Tarver said via the team’s official website. “’Hey guys, we all know this call, right? Well, you two guys are going to switch.’ Now, to an offense, it looks totally different because somebody is blitzing and somebody is dropping and it’s the same call to everybody else.”

Complicated Simplicity

How have the Raiders built a defense that both looks complex to the offense and is simple for them to execute? The simple answer is to have several players who are position flexible, meaning that they can rush or drop into coverage.

On this play near end of the first quarter, the Raiders get a sack on Smith by having seven players rush the quarterback. Prior to the snap, there is almost no way Smith can distinguish which four rushers are coming on the blitz and how the coverage will rotate.

In this iteration of the play, the cornerback blitzes, both linebackers loop around the left end and one of the safeties sprints back to provide deep help. The idea was to attack rookie right tackle Eric Fisher.

Here's an example of how the Raiders could run that same play but with the safeties swapping coverage responsibilities. To the quarterback, this coverage looks a little different, and he has to make the read after the snap with seven rushers coming into his face.

As Tarver said, it's the exact same call for the defense but if a couple players flip. The above was an example of how a play can be adapted to look complicated when only one or two things are changed.

In addition to rotating the coverage around, several different players can rush the quarterback. Maybe one safety blitzes, the other drips into coverage.

Maybe the other cornerback blitzes, one safety drops into deep coverage and the other draws man coverage underneath on the wide receiver.

Perhaps the cornerback doesn't blitz at all and two of the three safeties blitz, one around the edge to wreck the same havoc as would the cornerback blitz.

In this example, the safeties switch assignments, and the linebacker and the blitzing safety switch rush gaps. It's still an identical play, but it looks different in each different variation.

The possibilities are nearly endless, and it's the exact same call. It may be an extreme example because the offense might come out in a different formation, but it's exactly how Tarver has designed his defense.

Later in the game, the Raiders used the same personnel but didn't blitz a single player. The Raiders dropped eight into coverage, but they made sure to show blitz pre-snap.

Smith ended up panicking in the pocket as if a blitz was coming, and the result was a punt on the next play. Had Smith been able to stick in the pocket just a hair longer, he may have seen his receiver open on the deep post.

Oakland's defense doesn't have to learn something complicated; it just needs to learn the defensive calls. The Raiders don't have great players on defense, but they do have versatile, smart players who are starting to grasp the genius behind the scheme.

The key to the defense is still execution, but the Raiders are putting their players in position to make plays. Sunday's game against the Steelers could pose a challenge, but it's worth noting they have the second-worst offense the Raiders have played all season.