I would have suggested the Washington Sentinels, but I'm not sure if that was already trademarked.
Other than that, some sort of pirate theme would have been cool. The Bucs and the Raiders already have that. Here's a thesaurus entry for synonyms for pirates, since "Pirates" obviously won't work since it's taken. Some thesaurases include privateer, but here's one with some interesting examples.
noun:
buccaneer
raider
rover
filibuster
maurader
corsair
sea wolf
freebooter
sea robber
sea rover
The Washington Filibusters. I mean - it might work.