Expostulate, or go off, when the pets romp outside (7)
I believe the answer is:
protest
'expostulate' is the definition.
(thesaurus)
'go off when the pets romp outside' is the wordplay.
'go off' becomes 'rot' (as in food going off).
'when' becomes 'e' (I've seen this in other clues).
'the pets romp' becomes 'pst' (I can't justify this - if you can you should give a lot more credence to this answer).
'outside' means one lot of letters goes inside another (some letters go outside others).
'rot'+'e'='rote'
'rote' placed within 'pst' is 'PROTEST'.
'or' acts as a link.
Can you help me to learn more?
(Other definitions for protest that I've seen before include "Disapprove" , "State objection" , "Object strenuously" , "Showing support" , "Express opposition" .)