The underlined adjectival phrase in the sentence is "of the basketball game". The noun modified by this phrase is "start".
To identify the noun or pronoun modified by the underlined adjectival phrase, we need to locate the underlined adjectival phrase in the sentence. The underlined adjectival phrase is "of the basketball game." This phrase is modifying the noun "start." Therefore, the noun modified by the underlined adjectival phrase is "start."