Informal voters did their best! (6)
I believe the answer is:
strove
'best' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives sometimes define each other.
'informal voters did' is the wordplay.
'voters' anagrams to 'STROVE'.
Though, I'm not sure how this is indicated.
'their' is the link.
Can you help me to learn more?
(Other definitions for strove that I've seen before include "Voters (anag) - made every effort" , "Struggled" , "Endeavoured" , "Made great efforts" , "Tried hard for voters" .)