Final answer:
The verb in the sentence 'The pennant was won by the Red Sox' is in passive voice. It can be rewritten in active voice as: 'The Red Sox won the pennant.'
Step-by-step explanation:
The verb in the sentence 'The pennant was won by the Red Sox' is in passive voice. In a passive voice construction, the subject of the sentence (the pennant) is acted upon by the verb (was won). It follows the typical passive construction which includes a form of the be verb (was) combined with the past participle of the main verb (won), and the real doer of the action may be introduced by the preposition 'by' (by the Red Sox).
To rewrite the sentence in active voice, you make the doer of the action (the Red Sox) the subject of the sentence: 'The Red Sox won the pennant.'