The nickname is a back-formation from the school's yell, "wa-hoo-wa."
Official University of Virginia sports documents explain that Washington and Lee baseball fans first called University of Virginia players "a bunch of rowdy Wahoos," and used the "Wahoowa" yell as a form of derision during the in-state baseball rivalry in the 1890s, presumably after hearing them yell or sing "wa-hoo-wa." The term "Wahoos" caught on around the University and was commonly in use by the 1940s. "'Hoos" has emerged as an equally common accepted nickname throughout Grounds in student publications. In recent years, the Hoos nickname has become a nickname used by students and recent alumni of the University, and it is also commonly used in the media in reference to U.Va. sports teams.