Rio Ferdinand
Ferdinand was one of the top defenders of the 2010s. He captained Manchester United and also represented the English national soccer team with great pride. The center-back enjoyed great success as he won many honors including Premier League and Champions League titles.

After he retired he decided he wanted to become a professional boxer. The then-39-year-old committed himself to train and wanted to make his debut. However, the British Board of Boxing Control refused to license him because of his age and lack of experience (via The Sun).