What started as a pregame goof has turned into a full-fledged trademark battle for Baltimore Ravens linebacker Terrell Suggs.

During the player introductions segment of the Ravens’ nationally televised game against the Pittsburgh Steelers on Nov. 6, Mr. Suggs decided to have a little fun with the standard format of the segment, in which players state their name, position and alma mater. Instead of Arizona State University—where Mr. Suggs actually went to school until he was drafted into the NFL in 2003—the four-time Pro Bowl linebacker identified himself as “Sizzle,” an alumnus of “Ball So Hard University.”

Three days later, entrepreneur and Baltimore resident Brian Bussells submitted an application to trademark the faux university for a line of T-shirts, hats and other memorabilia. Mr. Bussells already has begun selling the merchandise through his website, BallSoHardU.com. His application included a slightly different design and sample product from the merchandise sold on his website, which feature a white university logo over purple or black fabric, with a silhouette of a defensive player tackling a quarterback in the center of the design. The design also indicates that the fictional university was established in 1996, the year the Ravens began playing in Baltimore.

However, Mr. Suggs—through his company, Team Sizzle Worldwide—also has been selling merchandise emblazoned with the “Ball So Hard University” tagline for some time, and filed his own trademark application for the phrase 10 days after Mr. Bussells submitted his.

In December, Mr. Bussells received a cease-and-desist letter from Team Sizzle’s attorneys, claiming that his clothing line could too easily be confused with the one marketed by Mr. Suggs, and that the merchandise violates the linebacker’s right to publicity. However, Mr. Bussells’ website remains open, with a disclaimer at the top indicating that the merchandise is in no way endorsed or affiliated with Mr. Suggs or the Ravens organization.