A contemptible person on a hill, one causing trouble (8)
I believe the answer is:
agitator
'one causing trouble' is the definition.
(I've seen this before)
'a contemptible person on a hill' is the wordplay.
'contemptible person' becomes 'git' (git can mean an annoying person).
'on' means one lot of letters go next to another.
'hill' becomes 'tor' (tor is a kind of hill).
'a'+'git'+'a'+'tor'='AGITATOR'
(Other definitions for agitator that I've seen before include "Stirrer up of public feeling" , "revolutionary" , "cause of trouble" , "One whipping up concern" , "One causing trouble" .)