Give up supporting attempt (5)
I believe the answer is:
forgo
'give up' is the definition.
(I know that give up can be written as forgo)
'supporting attempt' is the wordplay.
'supporting' becomes 'for' (being for something means supporting it).
'attempt' becomes 'go' (go is a kind of attempt).
'for'+'go'='FORGO'
(Other definitions for forgo that I've seen before include "Abjure" , "Sacrifice" , "Go without (something)" , "Relinquish, give up" , "pass up" .)