Harass Cambridge head in dark blue truck (9)
I believe the answer is:
persecute
'harass' is the definition.
('persecute' can be a synonym of 'harass')
'cambridge head in dark blue truck' is the wordplay.
'head' suggests taking the first letters.
'in' is an insertion indicator.
'dark blue' becomes 'perse' (a shade of greyish blue).
'truck' becomes 'ute' (Australian abbreviation for utility vehicle).
The first letter of 'cambridge' is 'c'.
'perse'+'ute'='perseute'
'c' put into 'perseute' is 'PERSECUTE'.
(Other definitions for persecute that I've seen before include "victimise" , "Persistently harass" , "Harass for reasons of politics, religion etc" , "Oppress, cause to suffer" , "hound" .)