Risks ducking head, by god! (5)
I believe the answer is:
dares
'risks' is the definition.
(I've seen this before)
'ducking head by god' is the wordplay.
'head' indicates taking the first letters.
'by' is a charade indicator (letters next to each other).
'god' becomes 'ares' (Greek god of war).
The initial letter of 'ducking' is 'd'.
'd'+'ares'='DARES'
(Other definitions for dares that I've seen before include "Has the courage to do brave or dangerous thing" , "''Who ..., wins'' (SAS motto)" , "Risks" , "Makes bold, challenges" , "Ventures" .)