European act upset animal (7)
I believe the answer is:
polecat
'animal' is the definition.
(I've seen this before)
'european act upset' is the wordplay.
'european' becomes 'pole' (someone from Poland).
'upset' indicates anagramming the letters.
'act' with letters rearranged gives 'cat'.
'pole'+'cat'='POLECAT'
(Other definitions for polecat that I've seen before include "Smelly animal" , "Kind of weasel, called skunk in America" , "Malodorous carnivore" , "weaselly type" , "Weasel-like creature" .)