This weekend, the Steelers’ Ben Roethlisberger will attempt to become the first rookie quarterback ever to take his team to the Super Bowl. Roethlisberger has yet to lose a game since taking over Pittsburgh’s starting job back in the third week of the season, and a trip to the Super Bowl would crown his season as the greatest ever by a first-year starting quarterback.

Other rookies have thrown for more yards and touchdowns, but Roethlisberger’s average of 8.9 yards per pass attempt is the highest in history by a quarterback in his first season as a starter; in fact, that number has been bested by only seven other quarterbacks in the past 25 years. And the only first-time starter to top Roethlisberger’s 66.4% completion rate was Chad Pennington in 2002. A list of similar performances (see attached table) by first-year starters shows Roethlisberger on the heels of Super Bowl champions like Joe Montana and Brett Favre.

Still, Roethlisberger’s shaky performance against the Jets last week led football pundits to wonder whether the pressure of the playoffs had rattled the rookie. His throws, once confident and pinpoint, were wobbly and inaccurate. He also locked onto single receivers without attempting to fool the defense into covering others, allowing the Jets to anticipate and step in front of his passes.

In the end, the Steelers’ superior defense and unstoppable running game – not to mention Doug Brien – gave Roethlisberger a chance to redeem himself in overtime. This points to one of the major reasons for Roethlisberger’s success: He has never been asked to carry his team.

Bill Cowher’s Steelers have run the ball far more than any other team in the league. Fifty-nine percent of the Steelers’ offensive plays were runs, and both Jerome Bettis and Duce Staley topped 800 yards on the ground for the season. Due in large part to Pittsburgh’s dominant running game, Roethlisberger only had to throw 22 passes per start.

On the other side of the ball, the Steelers held opponents to a league-best 258 yards per game. Thanks to defensive stops and forced turnovers, as well as strong kickoff and punt returns, Pittsburgh’s offense began its average drive at its own 33-yard line, good for third in the NFL.

So if rushing and defense were so important to the 15-1 Steelers, does Ben Roethlisberger really deserve the credit that he’s received for the team’s success? Well, according to Football Outsiders’ Points Above Replacement ratings – which break down each play of the season and compare each player’s value to a replacement-level player in the exact same set of situations, adjusted for opponent – Roethlisberger only ranks 10th among NFL quarterbacks in total value.

Roethlisberger’s lower value is partly due to the fact that he played only 14 games and threw fewer than 300 passes. Compare him to other quarterbacks based on his value per pass, and only Peyton Manning and Tom Brady were better in 2004.

Indeed, the legend of Ben Roethlisberger, the rookie who plays like a veteran, was built on his ability to lead the Steelers to a series of fourth-quarter comeback victories. In Week 6 against Dallas, Roethlisberger drove the Steelers to two touchdowns in the final quarter for a 24-20 win. Against Jacksonville in Week 12, the Steelers took the ball at their 25-yard line with less than two minutes left and a two-point deficit, and Roethlisberger led a drive to Jacksonville’s 19-yard line for the winning field goal. Big Ben also led a 67-yard fourth-quarter touchdown drive to beat the Giants 33-30 in Week 15, and his late heroics paved the way for both Pittsburgh wins over the Jets this season.

Of course, he almost deprived himself of the chance to lead a winning overtime drive Sunday against the Jets because of an interception he threw late in the fourth quarter. That play is emblematic of Roethlisberger’s struggles in the second half of the season. Through his first seven games, he threw only four interceptions and was sacked only seven times; in his last eight games, including the playoffs, he has thrown nine interceptions and been sacked 24 times in his last eight games.

Why has this happened? When the season began, the Steelers limited their playbook to a simple set of plays designed so that their rookie could thrive. It could be that Roethlisberger’s second-half struggles have their roots in the Steelers opening up that playbook a little faster than he can handle.

As for last week’s embarrassing performance, the Steelers deny press reports of a thumb injury. If instead, Roethlisberger’s subpar game was just the product of good old-fashioned nerves, the Steelers better get calm down their rookie by next Sunday.

Against the Patriots, Roethlisberger will face a defense designed to confuse him and take advantage of any hesitation. While he had a strong game the first time he played New England, Bill Belichick’s Patriots are 13-0 over the past four years when they face the same quarterback for the second time in a season.

But if Big Ben is seeking inspiration, he need only to look over at the other sideline. For while no rookie quarterback has ever led his team to the Super Bowl, Tom Brady did lead the Patriots to the big game in his first year as the starter. Statistically, Brady’s 2001 season was quite similar to Roethlisberger’s 2004 season. Roesthlisberger can only hope that his season ends the same way.

Mr.Schatz is the editor in chief of FootballOutsiders.com.