Harass spy on the way (6)
I believe the answer is:
molest
'harass' is the definition.
(I've seen this before)
'spy on the way' is the wordplay.
'spy' becomes 'mole' (I've seen this before).
'on' means one lot of letters go next to another.
'the way' becomes 'st'.
'mole'+'st'='MOLEST'
(Other definitions for molest that I've seen before include "Maliciously interfere with" , "Disturb, interfere with" , "Harry" , "Accost in motels" , "Bug" .)