Flipping moment unruly adolescent's let out (7)
I believe the answer is:
emitted
'let out' is the definition.
(to emit is to let out or release)
'flipping moment unruly adolescent's' is the wordplay.
'flipping' says the letters should be written backwards.
'moment' becomes 'time' (time is a kind of moment).
'unruly adolescent' becomes 'Ted' (reference to Teddy Boy subculture).
'time' in reverse letter order is 'emit'.
'emit'+'ted'='EMITTED'
(Other definitions for emitted that I've seen before include "Expelled" , "Put out" , "Gave out" , "Discharged" , "Sent forth" .)