FROM MSU WEBSITE:
The most popular legend is that during a home football game between State and arch-rival Mississippi, a jersey cow wandered onto the playing field. Mississippi State soundly whipped the Rebels that Saturday, and State College students immediately adopted the cow as a good luck charm. Students are said to have continued bringing a cow to football games for a while, until the practice was eventually discontinued in favor of bringing just the cow's bell.
Whatever the origin, it is certain that by the 1950s cowbells were common at Mississippi State games, and by the 1960s were established as the special symbol of Mississippi State. Ironically, the cowbell's popularity grew most rapidly during the long years when State football teams were rarely successful. Flaunting this anachronism from the 'aggie' days was a proud response by students and alumni to outsider scorn of the university's 'cow college' history.
In 1974, the SEC adopted a rule against artificial noisemakers that made it illegal to ring a cowbell during games. Despite creative efforts by MSU fans to circumvent the ruling and continue the tradition, the ban was in effect until 2010.
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The whole reason and tradition of the cowbell is built on ringing it in the face of opposition.
I'd add that it could come in handy in case shiit goes down after a game as well. Not that I would know* But I'd rather be carrying a bell than a pom pom or flag or roll of toilet paper.
