Step over vermin (4)
I believe the answer is:
pest
'vermin' is the definition.
'step over' is the wordplay.
'over' indicates an anagram.
'step' anagrammed gives 'PEST'.
(Other definitions for pest that I've seen before include "Annoyance" , "Constant nuisance" , "Troublesome man or animal" , "Annoying person" , "Troublesome person" .)