Struggle when genoa is fluttering (7)
I believe the answer is:
agonise
'struggle' is the definition.
('struggle'->'agonize' is in my internal thesaurus and 'ize'->'ise')
'genoa is fluttering' is the wordplay.
'fluttering' is an anagram indicator.
'genoa'+'is'='genoais'
'genoais' anagrammed gives 'AGONISE'.
'when' is the link.
(Other definitions for agonise that I've seen before include "Be very worried" , "Suffer great pain over something" , "Be in torments of indecision" , "Struggle mentally" , "Suffer torment" .)