He seeks to damage vehicle fellow reversed (6)
I believe the answer is:
vandal
'he seeks to damage' is the definition.
(person who damages things)
'vehicle fellow reversed' is the wordplay.
'vehicle' becomes 'van' (van is a kind of vehicle).
'fellow' becomes 'lad' (synonyms).
'reversed' says the letters should be written in reverse.
'lad' reversed gives 'dal'.
'van'+'dal'='VANDAL'
(Other definitions for vandal that I've seen before include "One of those who sacked Rome in 455" , "Old German" , "destructive member of the public" , "Defacer or wrecker" , "Wanton wrecker" .)