"He was captain of the team" is perfect English. No definite article is necessary or idiomatic. "He was the team captain" OR "He was team captain" also correct. Inserting the definite article presumes a context which is not indicated here, i.e. a question "was he the coach?" or the captain, goalie, etc. I am disappointed that the issue has not been addressed and corrected here; Danes have a reputation as the very best speakers of English as a second language.