The traditions page over at the official Marshall website has a good story about how the university first got it's name. Apparently, it was dubbed "The Thundering Herd" by Huntington Herald-Dispatch sportswriter Duke Ridgley in the 1920s. At that time, there was a popular Zane Grey novel by the same name, so it caught on fairly quickly. Ironically, a second sportswriter didn't like the name and spearheaded a campaign to get them known as the Boogercats instead, and at one time the students voted to dub the team the Green Gobblers. Good thing those efforts didn't quite work out, eh?
Traditions - The Marshall Thundering Herd - Official Athletic Site