Risk all to support the impecunious (2,3,5)
I believe the answer is:
go for broke
'risk all' is the definition.
(I've seen this in another clue)
'support the impecunious' is the wordplay.
'support' becomes 'gofor' (I can't explain this - if you can you should give a lot more credence to this answer).
'the impecunious' becomes 'broke' (I've seen this before).
'gofor'+'broke'='GO FOR BROKE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for go for broke that I've seen before include "Make an all-out effort" , "Make all-or-nothing effort" , "Gamble everything" , "Risk everything in an all-out effort" .)