Attack joke about old church (6)
I believe the answer is:
pounce
'attack' is the definition.
(I've seen this before)
'joke about old church' is the wordplay.
'joke' becomes 'pun' (pun is a type of joke).
'about' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'church' becomes 'ce' (abbreviation for Church of England).
'pun' going around 'o' is 'poun'.
'poun'+'ce'='POUNCE'
(Other definitions for pounce that I've seen before include "Jump or spring down as on prey" , "Spring or swoop down on to attack" , "Suddenly spring; fine powder" , "Act fast to take advantage" , "Jump swiftly on, as cat might" .)