Like "Super Bowl," "Olympics" and "NASCAR," "March Madness" is also a term that is protected by trademark law, and its unauthorized use in commercials could result in legal liability. But the development of March Madness is a bit more interesting, and you can probably thank Brent Musburger for that. The Illinois High School Association (IHSA) has been using the term "March Madness" to describe its state high school basketball tournament since the early 1940’s. Broadcaster Brent Musburger went to journalism school in Chicago, then worked for both a Chicago newspaper and television station, where he almost certainly covered that basketball tournament and was well aware of the term "March Madness." When he later began covering the NCAA basketball tournament for CBS in 1982, he naturally began referring to that tournament as "March Madness" as well.
As you know, the term caught on. It ultimately led to a trademark infringement suit in 1996, and that led to a joint venture between IHSA and NCAA, called the March Madness Athletic Association (MMAA) which now holds all trademark rights to the term "March Madness." In fact, they own 15 federal registrations containing that term, covering everything from the actual tournaments to broadcasting and webcasting the tournaments to mugs, T-shirts, towels, and even carbonated soft drinks.