Most reckless supports heartless robbery (8)
I believe the answer is:
brashest
'most reckless' is the definition.
Both the answer and definition are superlative adjectives. Maybe you can see a link between them that I can't see?
'supports heartless robbery' is the wordplay.
'supports' becomes 'bras' (I've seen this before).
'heartless' suggests removing the centre.
'robbery' becomes 'heist' (heist is a kind of robbery).
'heist' with its middle taken out is 'hest'.
'bras'+'hest'='BRASHEST'
Can you help me to learn more?
(Other definitions for brashest that I've seen before include "Most brazen" , "Flashiest and loudest" .)