One script upset controller (9)
I believe the answer is:
inspector
'controller' is the definition.
(I've seen this before)
'one script upset' is the wordplay.
'upset' indicates an anagram.
'one'+'script'='onescript'
'onescript' is an anagram of 'INSPECTOR'.
(Other definitions for inspector that I've seen before include "reviewer" , "controller" , "bluebottle!" , "Police officer" , "Lestrade for instance" .)