Gangster gets into it for political arrangement (9)
I believe the answer is:
coalition
'political arrangement' is the definition.
(alliance between two parties)
'gangster gets into it' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'gets into' is an insertion indicator.
'it' becomes 'coition' (another term for coitus - 'it' can mean sex).
'al' inserted inside 'coition' is 'COALITION'.
'for' acts as a link.
(Other definitions for coalition that I've seen before include "Temporary alliance" , "form of government" , "Alliance of parties" .)