Cause of bad luck gangster loves? (6)
I believe the answer is:
hoodoo
'cause of bad luck' is the definition.
(I've seen this before)
'gangster loves?' is the wordplay.
'gangster' becomes 'hood' (I've seen this in another clue).
'loves?' becomes 'oo' (love means 0 in tennis).
'hood'+'oo'='HOODOO'
(Other definitions for hoodoo that I've seen before include "Thing or person thought to cause bad luck" , "Fetish - charm with magical powers" , "Thing or person that brings bad luck" , "Jinx" , "Spells" .)