Police officer caught on fast? (9)
I believe the answer is:
constable
'police officer' is the definition.
'caught on fast?' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'fast?' becomes 'stable' (fast can mean secure).
'c'+'on'+'stable'='CONSTABLE'
(Other definitions for constable that I've seen before include "CARRY ON FILM" , "British painter and police officer" , "Artist; police officer" , "In England, a great painter or lowly policeman" , "Bobby" .)