Here's why:
* Participial Phrases: These are phrases that begin with a participle (a verb form ending in -ing or -ed) and function as adjectives, modifying a noun or pronoun.
* "Overcome" is the past participle of the verb "overcome" and acts as an adjective modifying the noun "audience".
The complete phrase "Overcome by emotion" describes the audience's state, making it a participial phrase.