Dangerous section of reef, as nutters recalled (6)
I believe the answer is:
unsafe
'dangerous' is the definition.
(I know that dangerous can be written as unsafe)
'section of reef as nutters recalled' is the wordplay.
'section of' indicates a hidden word.
'recalled' says the letters should be written backwards (to recall can mean to bring something back).
'efasnu' can be found hidden inside 'reef as nutters'.
'efasnu' backwards is 'UNSAFE'.
(Other definitions for unsafe that I've seen before include "Unreliable" , "giving no protection" , "Dangerous, insecure" , "Perilous" , "Dangerous - legally without basis" .)