WASHINGTON - Washington Redskins coaches don't need to wait until game day to realize there's a stark difference between Clinton Portis, the team's injured star running back, and Rock Cartwright, their able-bodied replacement.

On Wednesday, as the team began installing its game plan for today's game against the Eagles at Lincoln Financial Field, Cartwright hit the practice field as the Redskins' latest starting running back, nearly four inches shorter than Portis but still strong in other areas.

"Everybody on the team calls him 'Big Heart,' because he plays with such a big heart," center Casey Rabach said. "He may not be the most talented of running backs, but he's going to give the most effort of anybody you'll see."

Truth be told, taking reps with the starters Wednesday was a bit frustrating for Cartwright, who hasn't started a game since 2003. Usually, either Portis or Ladell Betts, who was placed on injured reserve Monday, practices with the Redskins' starters, and Cartwright, the team's kickoff-return specialist since 2006, lines up as a running back for the scout team, mimicking the plays and formations of the next opponent.

On Wednesday, Cartwright had just two reps with the scout team, which means practice ended in the afternoon, and Cartwright didn't feel like he got enough work in.

"I had to go do some extra running after practice to make sure I'll be conditioned for Sunday," he said.

Redskins coach Jim Zorn said that though Cartwright will be the team's primary back today, he expects to rotate Cartwright, Quinton Ganther, and Marcus Mason, who was signed Monday as the team's third running back.