By Steve Silverman-

(CBS) The stars are changing in the NFL this season.

A year ago, Aaron Rodgers, Drew Brees and Tom Brady were the unquestioned leaders at the quarterback position.

All three were in the prime of their careers and there was no reason to believe that any of them would slip from their lofty spots in the NFL penthouse.

However, through the first five weeks of the season, only Brady is near the top of the NFL’s passer ratings. The top five quarterbacks in the league – at least according to the NFL’s long-maligned but strangely effective rating system – are Alex Smith, Matt Ryan, Brady, Peyton Manning and Robert Griffin III.

Rodgers was seemingly on his way to Hall of Fame acclimation last year. He is the 8th-ranked quarterback in the league this season, while Brees has slipped all the way to 13th.

It’s easy to make a case why Smith and Ryan have climbed the charts so dramatically. It’s a bit more difficult to figure out why Rodgers and Brees have fallen to this point in the season.

Smith has come into his own under head coach Jim Harbaugh. Prior to Harbaugh’s arrival in San Francisco, Smith was just a place-holder at the quarterback position for previous head coaches Mike Nolan and Mike Singletary.

Both coaches ostensibly asked Smith to be a game manager and not make mistakes. The negative implication was obvious to Smith and every time he took a step forward, he would take two steps back.

Harbaugh came in and realized that he was going to turn the offense over to Smith – with a lot of help from running back Frank Gore. That 1-2 punch got the 49ers to the NFC Championship Game last year.

This year he has brought in go-to wide receiver Mario Manningham, and Michael Crabtree has rapidly turned into a star. Vernon Davis was already there. When Smith can turn and hand the ball off to Gore, or take one of the three primary receiving options, he becomes a dangerous passer capable of dominating the NFL.

Ryan took a lot of abuse in the offseason because of his unfulfilling resume when it comes to playing postseason football. Ryan and head coach Mike Smith have not won a playoff game and they know they are under the gun.

Ryan has put sensational numbers on the board this season. He is averaging 301.4 yards per game and he has thrown 13 touchdowns to just three interceptions. Why the improvement from good quarterback to elite? How about the improvement of wide receiver Julio Jones.

Jones is an unstoppable force at wide receiver because of his speed and strength. Combined with Roddy White, Ryan knows he will always have at least one open receiver and he has taken advantage of it.

Brady is in his regular place, and has mastered the Patriots’ fast-paced no-huddle offense. By shouting one word after the previous play ended, Brady sets the New England offense in motion.

Within three seconds, the Patriots’ offense is off and running while the defense is trying to recover. This has given Brady a huge advantage and he is completing 67.0 percent of his passes and throwing for 290 yards per game.

On the downside, Rodgers is not getting enough time from his offensive line. He is under constant pressure and that is forcing him to throw the ball without setting his feet the way he would like. Instead of moving towards his target so he can zip the ball into the numbers of his receiver, he is flipping the ball off of his back foot. His passes are lacking velocity and accuracy – at least compared to last year.

Rodgers and head coach Mike McCarthy can correct this problem with improved blocking from the offensive line, but the Packers’ one-dimensional offense is not likely to change. They have no running game and the defense does not have to respect that part of the Packers’ offense.

The biggest change for Brees is his loss of accuracy. Last year he completed 71.2 percent of his passes. This year, he is only completing 58.9 percent of his throws. While Brees threw a touchdown in his 48th straight game (breaking Johnny Unitas’s record) in the Saints Week 5 win over the Chargers, he has not had the time from his offensive line and his receivers have not been getting open the way they had in the past.

Suspended head coach Sean Payton is not around to figure out how to overcome this issue and it doesn’t appear the current Saints brain trust will give Brees the answer he needs to overcome the problem.

Steve Silverman

Steve Silverman is an award-winning writer, covering sports since 1980. Silverman was with Pro Football Weekly for 10 years and his byline has appeared in the Wall Street Journal, Playboy, NFL.com and The Sporting News. He is the author of four books, including Who’s Better, Who’s Best in Football — The Top 60 Players of All-Time. Follow him on Twitter (@profootballboy) and read more of his CBS Chicago columns here.