The Steelers worked out two free-agent centers yesterday at Saint Vincent College in Latrobe, and they received some good news on the injured left knee of Darnell Stapleton.

Coach Mike Tomlin said after practice last night at Latrobe Stadium that Stapleton will miss "a couple of weeks" after arthroscopic surgery on his left knee yesterday.

Tomlin called it "exploratory surgery" and said they would let him rest for two weeks and see how his body responds. Tomlin ruled out placing Stapleton on injured reserve, which would end his season.

Alex Stepanovich, a six-year veteran who played for the Atlanta Falcons last season, and rookie Alex Derenthal of Temple worked out for the team and then left the campus by midafternoon.

Stepanovich, who played at Ohio State and was a fourth-round draft pick and former starter for the Arizona Cardinals, was released by the Falcons in June. Derenthal signed as an undrafted rookie with the New York Giants but was released before the start of their training camp.

Stapleton became the starting right guard last season, but he was playing center at the start of training camp because of Justin Hartwig's toe injury.

Tomlin said that Hartwig should be ready to resume practice soon. The Steelers have only two healthy centers, First-year pro Doug Legursky and rookie A.Q. Shipley, neither of whom have played in an NFL regular-season game.

Quarterback Charlie Batch has staked his claim as the only native Pittsburgher to earn two Super Bowl rings with the Steelers. He swears he researched it.

Never mind that Batch grew up in Homestead, which may be in Allegheny County but is not part of the city of Pittsburgh. And what about Jack Ham, a Johnstown native with four Super Bowl rings? Or Terry Hanratty, who hails from Butler and has Super Bowl rings from the 1974 and '75 Steelers seasons?

"That's not Pittsburgh," Batch declared. "That's too far."

Among the things the Steelers are stressing this training camp is for their defensive backs to hang onto interceptions. The Steelers made great strides last season by intercepting 20 passes, up from 11 in 2007.

The cornerbacks, however, did not contribute much to that number. Safety Troy Polamalu led the team with seven interceptions. The cornerbacks combined for six, with nickel corner Deshea Townsend and departed Bryant McFadden leading that group with two apiece.

"Troy was probably the only one who had a frequent number of picks," said linebacker James Farrior, captain of the defense. "We had a lot of opportunities, we just didn't catch it."

Defensive coordinator Dick LeBeau watched in one practice this week as rookie cornerback Joe Burnett and new starting left cornerback William Gay dropped consecutive interceptions. Coach Mike Tomlin said something after each, and Gay's defensive teammates got on him, too.

"You get one or two opportunities in a game to impact a game," LeBeau said. "Those are impact plays, turnovers. You want to get it done on the practice field or you're not going to get it done on Sunday."

Hines Ward and Polamalu returned to practice and went through all the drills last night. Neither had practiced since Saturday. ... An estimated 15,000 attended practice last night, the largest crowd since the Steelers have been holding these annual practices in downtown Latrobe. ... The largest cheer of the night came when Polamalu intercepted Ben Roethlisberger's first pass in an 11-on-11 drill.