Deliberately unreasonable (8)
I believe the answer is:
perverse
'deliberately unreasonable' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for perverse that I've seen before include "Deliberately difficult" , "Deliberately departing from what is reasonable" , "Deliberately contrary" , "Obstinately wrong-headed" , "Preserve in order to be stubbornly intractable" .)