A Fragment phrase can be defined as a sentence that resembles a sentence but lacks delivering a complete idea. This sentence serves as a dependent clause in a sentence.
The given sentence is an example of a fragment phrase or sentence. Though the phrase appears to be a sentence but it lacks complete idea because we don't know about which 'people' is it talking about.
a time when i defended myself in an argument was when the police thought that i had stole something from the store so i argued my way out of the situation