Clinton Portis is a good runner, maybe the best back in the league right now, but his style is not the type that gives the Ravens problems. Portis is more of a one cut, downhill type runner, and also a threat out of the backfield.
But with the exception of Giants running Brandon Jacobs, the Ravens have had huge success against these types of downhill runners. Jacobs in the only running back I've ever seen intimidate the Ravens.
Plus, Portis won't have success because the Redskins can't run inside. Ravens DT Haloti Ngata can't be handled by Redskins' center Casey Rabach.