Beef will go off; that's the nuisance about it (7)
I believe the answer is:
protest
'beef will' is the definition.
'protest' can be an answer for 'beef' (thesaurus). I'm not sure about the 'will' bit.
'go off that's the nuisance about it' is the wordplay.
'go off' becomes 'rot' (I've seen this before).
'that's the nuisance' becomes 'pest' (I've seen this before).
'about it' is an insertion indicator.
'rot' placed inside 'pest' is 'PROTEST'.
Can you help me to learn more?
(Other definitions for protest that I've seen before include "Showing support" , "Public demonstration" , "Objection from potters" , "Complaint" , "Statement or action showing disapproval" .)