Three things the Steelers will be watching tonight against the Panthers:

1. The battle at free safety between Ryan Clark and Tyrone Carter

2. Can Duce Staley be effective as the No. 2 back.

3. The battle for the third quarterback spot between rookie Omar Jacobs, a fifth-round draft pick, and second-year player Shane Boyd (left).

If familiarity counts for anything, Tyrone Carter will be the starter at free safety when the Steelers open their regular season next week against the Miami Dolphins. That has been one of the reasons Brett Keisel has been able to slide into the right defensive end spot for Kimo von Oelhoffen, who left in free agency.

		TODAY Game: Panthers vs. Steelers, 7:30 p.m. Where: Heinz Field. TV/radio: KDKA/WDVE-FM (102.4) and WBGG-AM (970). Related coverage Steelers sign Parker to a four-year, $13.6 million contract Holmes' trial rescheduled Steelers Notebook: Cowher lauds Batch's work

But, when the Steelers (0-3) conclude their preseason tonight against the Carolina Panthers (3-0) at Heinz Field, it will be newcomer Ryan Clark who gets his second chance to start at free safety -- the final audition in what has been a weekly rotation to find the replacement for Chris Hope, who also departed in free agency. With a number of starters expected to sit out the game tonight -- including quarterback Ben Roethlisberger and running back Willie Parker, who received a new four-year, $13.6 million contract yesterday -- the battle at free safety is one of the few subplots that remain.

But it is not the only one:

Duce Staley, who will start the game for Parker, needs to convince the coaches he can be an effective No. 2 back in the offense, especially after missing 17 games in his previous two seasons with the Steelers.

Staley, who has rushed for 46 yards on 23 carries in the preseason, is not in much danger of being among the final cuts when the roster is pared to 53 players Saturday. But the Steelers probably will scour the waiver wire for a veteran running back after NFL teams reduce their rosters this weekend.

Rookie Omar Jacobs and first-year free agent Shane Boyd will split most of the playing time against the Panthers in an attempt to determine if either is equipped to make the 53-man roster as the No. 3 quarterback. If not, the Steelers will consider the possibility signing a veteran quarterback, if they see one they like among the final cuts. Boyd is expected to replace Charlie Batch, who will start for Roethlisberger, sometime in the second quarter.

The Steelers did not have to replace any starters on defense last season. This year, though they have two departures -- Hope and von Oelhoffen.

Keisel, a seventh-round pick in 2002 and a pass-rush specialist, will step in for von Oelhoffen.

Carter, a holdover from the Super Bowl team last season, and Clark, the only major pickup in free agency, are battling for the only starting position that has not been determined. They have split time with the first-team defense in training camp, and each has been given two starts in the preseason.

"The main thing," said Carter, who spent most of last season playing as the sixth defensive back in the team's quarter defense, "is you got to win over your teammates and let them know they can be confident in you and believe in you as well."

That has probably been easier for Carter because he has been with the Steelers for two seasons. Clark, who played opposite Sean Taylor in the Washington Redskins' secondary, is a newcomer who admitted he was nervous in his first preseason start against the Minnesota Vikings because he wanted to impress his new teammates.

"They haven't seen him. They haven't seen what he can do," Carter said.

"That always goes back in your mind. But, at the same time, it can help [Clark] to be more conscious, more alert, out there, let them know, 'Hey, you guys can believe in me. I can do this here.' "

Keisel said that's one of the reasons he believes the defense will make an easy transition after von Oelhoffen's departure: His teammates' familiarity with him as a player in pass situations and special teams.

"They're much more comfortable with me in the huddle than, say, Ryan, just because this is his first year here and this is my fifth," said Keisel, a seventh-round pick in 2002.

"I went out there as a reserve a few times [last year], so they're kind of used to seeing me out there."

Still, outside linebacker Clark Haggans said he had to prove his worth as a starter when he replaced Jason Gildon, the club's all-time sack leader (77), in 2004. And Haggans had spent two seasons as a backup and special-teams standout with the Steelers.

"You always want to prove something to your teammates," Haggans said. "We're all competitive."

They get one more chance -- perhaps a final one -- tonight.