Dorian’s active trespass (6)
I believe the answer is:
inroad
'trespass' is the definition.
(inroad is a kind of trespass)
'dorian's active' is the wordplay.
'active' indicates an anagram (the letters are active/moving).
'dorian' is an anagram of 'INROAD'.
(Other definitions for inroad that I've seen before include "Offensive" , "One's intrusive" , "Sudden attack made into a country" , "Incursion, raid" , "Encroachment, intrusion" .)