Was an upright representative (5)
I believe the answer is:
stood
'representative' is the definition.
The answer and definition are different parts of speech. However, adjectives and past participle verbs can occasionally define each other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for stood that I've seen before include "Rose to one's feet" , "Was upstanding" , "Was a candidate for election" , "Was situated" , "Remained valid" .)