Love upsetting animal (4)
I believe the answer is:
vole
'animal' is the definition.
(thesaurus)
'love upsetting' is the wordplay.
'upsetting' indicates anagramming the letters.
'love' anagrammed gives 'VOLE'.
(Other definitions for vole that I've seen before include "Fieldmouse" , "River-bank rodent" , "A small plant-eating rodent - love it" , "River bank rodent" , "A little rodent" .)