Religion doesn't start as a hit (4)
I believe the answer is:
slam
'a hit' is the definition.
(I know that slam is a more specific form of the action hit)
'religion doesn't start' is the wordplay.
'religion' becomes 'Islam' (Islam is a religion).
'doesn't start' means to remove the first letter.
'islam' with its first letter removed is 'SLAM'.
'as' acts as a link.
(Other definitions for slam that I've seen before include "Shut violently" , "A grand one is 13 tricks" , "Violently strike against" , "Crash (door closed)" , "Severely criticise; shut (a door) forcefully" .)