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Sean Mahan is the Steelers' biggest all-time, free-agent bust because of the historical implication of his performance.
Beginning with Ray Mansfield in 1964, only four players regularly started at center for the Steelers for 42 years. The last three, Mike Webster, Dermontti Dawson and Jeff Hartings, all made multiple Pro Bowls.
After Hartings retired following the 2006 season, the Steelers signed Mahan from the Tampa Bay Buccaneers to a five-year, $17 million contract.
Part of the reason the Steelers acquired Mahan was because new coach Mike Tomlin was familiar with him. He was on the Buccaneers' staff.
The problem was that Mahan could not uphold the Steelers' rich tradition at center. The Pittsburgh Post-Gazette said "he was overpowered by some of the bigger nose tackles in the league."
Mahan's ineffectiveness reached a whole new level in the playoffs when he committed a penalty that ultimately might have cost the Steelers the game.
In an AFC Wild Card Game at Heinz Field, the Steelers had narrowed a 28-10 Jacksonville Jaguars lead to 28-23 with about 10 minutes left in the game.
Ben Roethlisberger completed the two-point conversion pass to Hines Ward, which would have pulled the Steelers to within a field goal. But it was negated by Mahan's holding penalty. The Steelers attempted another two-point conversion after moving 10 yards back, and it failed.
The Steelers had to go for two when they scored another touchdown to go up 29-28. That attempt also failed, which allowed the Jaguars to win the game with a field goal.
The Steelers sent Mahan back where he came from, trading him to Tampa Bay before the 2008 season. He played two more seasons, starting four games in 2009.