It involved 70 people and three people were arrested.
Metro spokeswoman Cathy Asato said Saturday that five people were taken to the hospital with injuries.
The fight started about 11 p.m. Friday at the L'Enfant Plaza station, but officials are not sure what prompted the brawl.
Transit police charged an 18-year-old man with disorderly conduct. Two juveniles were also charged.
Asato says no weapons were found at the scene.