This is the 11551st most frequent Polish word.
kapitanem
"Kapitanem" means "captain" (instrumental case) in English.
In this sentence, "kapitanem" is used to indicate the role of captain in the football team, functioning as a noun in an instrumental case to describe Jan Kowalski's position.
Kapitanem drużyny piłkarskiej jest Jan Kowalski.
The captain of the football team is Jan Kowalski.
Here, "kapitanem" portrays the role as a captain of a ship, employed in an instrumental case to describe the professional occupation.
Przez rok pracował jako kapitanem statku.
He worked as the captain of a ship for a year.
In this instance, "kapitanem" represents a military rank, used in an instrumental case following the verb "mianowany" (appointed) to denote a change of status.