In grammar there are various types of complements. In grammar a complement "is a word or group of words that completes the predicate". In this case specifically, the complement has the function as a subject complement. The subject complement reflects who the subject is talking to (they complement). In this sentence we know that the coach gave few words of encouragement but we wanted to know to who and that is when the subject complement comes in hand (the team).
The answers would be "He sells some magazines" or "He decides he wants to be a writer.", since Gumption means to be resourceful or have spirited initiative.
