Strangely rude pet broke out (7)
I believe the answer is:
erupted
'broke out' is the definition.
('erupt' can be a synonym of 'break out')
'strangely rude pet' is the wordplay.
'strangely' indicates anagramming the letters.
'rude'+'pet'='rudepet'
'rudepet' is an anagram of 'ERUPTED'.
(Other definitions for erupted that I've seen before include "Blew up like volcano" , "Blew up or out as volcano may" , "Broke out suddenly" , "Broke out (like Etna)" .)