Crowd backed one short story to do with union (7)
I believe the answer is:
'to do with union' is the definition.
(relating to a marriage or union)
'crowd backed one short story' is the wordplay.
'crowd' becomes 'ram' (ram can mean to crowd or press into an area).
'backed' says the letters should be written backwards.
'one short story' becomes 'ital' (I can't explain this - if you can you should believe this answer much more).
'ram' reversed gives 'mar'.
Can you help me to learn more?
(Other definitions for marital that I've seen before include "Of a wedding" , "Conjugal" , "Of nuptials" , "Referring to a union" , "Maybe husband's" .)