Attack saint’s stupid fear (6)
I believe the answer is:
strafe
'attack' is the definition.
(I've seen this before)
'saint's stupid fear' is the wordplay.
'saint' becomes 'st'.
'stupid' indicates anagramming the letters (in a stupid order).
'fear' anagrammed gives 'rafe'.
'st'+'rafe'='STRAFE'
(Other definitions for strafe that I've seen before include "Attack with machine-gun fire" , "Attack with gunfire from the air" , "Attack with machine guns or cannon from a low-flying plane" , "Pepper" , "low attack" .)