Strange seeing OAP spying (9)
I believe the answer is:
espionage
'spying' is the definition.
(espionage is a kind of spying)
'strange seeing oap' is the wordplay.
'strange' indicates anagramming the letters.
'seeing'+'oap'='seeingoap'
'seeingoap' is an anagram of 'ESPIONAGE'.
(Other definitions for espionage that I've seen before include "agent's job" , "intelligence" , "undercover work" , "secret work" , "007's game" .)