Gathered in street before sinking in mire (8)
I believe the answer is:
mustered
'gathered' is the definition.
(mustering is a kind of gathering)
'street before sinking in mire' is the wordplay.
'street' becomes 'st' (abbreviation).
'before' says to put letters next to each other.
'sinking' becomes 'ere' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'mire' becomes 'mud' (synonyms).
'st'+'ere'='stere'
'stere' inserted within 'mud' is 'MUSTERED'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for mustered that I've seen before include "Caused to assemble" , "Marshalled" , "Brought together" , "Assembled, gathered together - say troops" .)