Four characters in Europe standing trial (4)
I believe the answer is:
pest
'trial' is the definition.
(both can mean an annoying person)
'four characters in europe standing' is the wordplay.
'four characters in' indicates a hidden word (four letters hidden in the clue).
'PEST' can be found hidden inside 'europe standing'.
(Other definitions for pest that I've seen before include "Disease with a high death rate" , "Infernal nuisance" , "Troublesome person" , "A nuisance - step on it" , "Destructive insect or other animal" .)