Flourish when unruly mob accepts defeat (7)
I believe the answer is:
blossom
'flourish' is the definition.
(I've seen this before)
'unruly mob accepts defeat' is the wordplay.
'unruly' is an anagram indicator.
'accepts' is an insertion indicator.
'defeat' becomes 'loss' (I've seen this before).
'mob' is an anagram of 'bom'.
'bom' placed around 'loss' is 'BLOSSOM'.
'when' acts as a link.
(Other definitions for blossom that I've seen before include "Flourish and prosper" , "better period results" , "Flower - flourish" , "Flowers (on tree, shrub)" , "Girl - flower(s)" .)