GMAT Verbal Section | Re: Why is this correct? The Pronoun 'Who'

I am watching the Subject-Verb Proximity video on Magoosh and, while the video is highlighting a different construction preference for the following statement, it also notes that this statement is grammaticallycorrect:

The new city supervisor was elected, who ran against Johnson, citing his corruption charges blah blah.

I have seen similar constructions as correct answers in practice guides. Is it really correct to have the pronoun 'who' after a verb and object?

Why is this correct?