Love to upset animal (4)
I believe the answer is:
vole
'animal' is the definition.
(thesaurus)
'love to upset' is the wordplay.
'to upset' indicates an anagram.
'love' anagrammed gives 'VOLE'.
(Other definitions for vole that I've seen before include "A small plant-eating rodent - love it" , "creature" , "River bank rodent" , "Small mammal - one to love" , "win all the tricks" .)