Soccer star Cristiano Ronaldo is in a trademark battle with fitness enthusiast Christopher Renzi from Rhode Island over the name “CR7.” Ronaldo goes by the moniker, and the Danish company behind Ronaldo’s underwear line argues that it holds the “exclusive, worldwide license” to the name and has demanded that Christopher Renzi give up his trademark to CR7.

Christopher Renzi does not intend to give up his trademark, which he registered in 2009 and has used to market clothing and a fitness workout video. Although Ronaldo is a more famous user, Renzi has been using the name in the United States and has registered it with the U.S. Patent and Trademark Office. Renzi filed suit in Rhode Island District Court to enforce his rights against Ronaldo’s clothing company and Ronaldo individually.

This case shows the importance of registering your trademarks. While fans may know Ronaldo by the CR7 moniker, Renzi registered the name five years ago and has been using it in business. Companies should not assume that a name or term they popularize is theirs for the taking if they do not take steps to claim it.