According to Texas A&M University's trademark application with the U.S. Patent and Trademark Office, the school has used the "12th Man" trademark in commerce to refer to its football fans continuously since 1922. The NFL's Seattle Seahawks, who began playing football in 1976, recently began referring to its fans as the "12th Man." As you would expect, this caused a dispute between the two over who owned the "12th Man" mark.
It is simple: Texas A&M owns the mark. The school used the mark in commerce before the Seahawks. The school did not file for the 12th Man mark until the 1990s, but this was still before the Seahawks began using the mark.
Accordingly, the Seahawks license the trademark from Texas A&M. If Texas A&M did not either license the mark to the Seahawks, or did not file an infringement action or seek an injunction to prevent the Seahawks from using the mark, Texas A&M would risk a naked license. This means the school unintentionally abandons the mark and loses its rights in it.