Cloak catching on for gangster (6)
I believe the answer is:
capone
'gangster' is the definition.
(Al Capone)
'cloak catching on' is the wordplay.
'cloak' becomes 'cape' (cape is a kind of cloak).
'catching' means one lot of letters goes inside another.
'cape' enclosing 'on' is 'CAPONE'.
'for' acts as a link.
(Other definitions for capone that I've seen before include "Italian-American gangster, d. 1947" , "Notorious criminal" , "Hood" , "Chicago gangster, d. 1947" , "Al - , notorious gangster" .)