Female team startled after loud siren (5,6)
I believe the answer is:
femme fatale
'siren' is the definition.
('femme fatale' can be a synonym of 'siren')
'female team startled after loud' is the wordplay.
'startled' indicates anagramming the letters.
'after' is a charade indicator (letters next to each other).
'loud' becomes 'f' (A musical term).
'female'+'team'='femaleteam'
'femaleteam' with letters rearranged gives 'emmefatale'.
'emmefatale' after 'f' is 'FEMME FATALE'.
(Other definitions for femme fatale that I've seen before include "attractive woman" , "Seductive woman who causes trouble" , "Vamp" , "Siren, bewitching woman" , "Temptress" .)