Ben Leber looked like he knew what he was doing Sunday against the Dallas Cowboys. And he was doing his business quicker. The fourth-year linebacker who just a few months ago wondered what his role would be at this point started his 36th consecutive game and had a sack and five tackles (two behind the line). Considering his issues in the past about getting in the backfield quickly enough, it was a standout performance. Leber spoke this week of having tweaked little things in his stance while learning to anticipate plays better. "I tried to eliminate some of the false steps I was making last year that would put me a half-step behind," he said. "The biggest thing this last game is I was able to anticipate plays a little more. There were times in the game I had narrowed it down to what they could run." There remains the specter of top draft pick Shawne Merriman, who eventually will be healthy and cognizant enough to challenge for the job he was brought in to do. For now, as Merriman is an unknown while still learning the defense, Leber remains the starter on the strong side. "It definitely feels good I've put myself in a position where their decision has to be a little tougher," Leber said. "It was my motivation going into this game, trying to establish myself yet again." Another shot Igor Olshansky, whose ankle and knee injuries prevented him from practicing again yesterday, is doubtful to play Sunday at Denver, which makes Luis Castillo's first NFL start likely. It will come a week after Castillo committed a crucial mistake, a roughing-the-passer penalty that ended up greatly aiding the Cowboys in their comeback. "Even a couple plays after that, you're back in there and you're like, 'I've got to make up for that,' " Castillo said. "I feel like I have to get to the quarterback every time. I'm excited to get back out there. "It killed me for a couple days. You feel like a horse's (rear end). You let down your team and did something that directly led to you losing the game. But you've got to move on." Rookie running back Darren Sproles, limited to kick returns last week, is being inserted in some different packages from scrimmage. "We're going to try to give him the ball a little more on offense," coach Marty Schottenheimer said. . . . Schottenheimer said Merriman could be used in a handful of situations at linebacker but reiterated he will primarily work on special teams. . . . Rookie receiver Vincent Jackson (calf) did not practice, and while he is listed as questionable, it appears unlikely he will play Sunday after not practicing for three weeks. . . . The Oakland and Buffalo games were announced as sellouts yesterday, and only 2,000 tickets remain for the Sept. 25 game against the New York Giants. That game probably will sell out, which would leave tickets for only the Dec. 11 game against Miami and the Dec. 31 regular-season finale against Denver.