The gerund phrase in the sentence "Before signing with the Brooklyn Dodgers, Jackie Robinson played football for a semiprofessional team in Hawaii" is "signing with the Brooklyn Dodgers."
A gerund is a verb form that ends in -ing and functions as a noun. In this sentence, the gerund phrase "signing with the Brooklyn Dodgers" functions as the subject of the main verb "played." It tells us what Jackie Robinson did before playing football for a semiprofessional team in Hawaii.
To identify the gerund phrase, we can ask ourselves the following questions:
1. What is the verb form that ends in -ing? (signing)
2. What is the function of this verb form in the sentence? (It functions as a noun, specifically as the subject of the main verb "played.")
3. What additional words are included with the verb form? (with the Brooklyn Dodgers)
Therefore, the gerund phrase "signing with the Brooklyn Dodgers" functions as the subject of the verb "played" and provides more information about Jackie Robinson's actions.