Comparatively shrewd one that might have quarrel (6)
I believe the answer is:
archer
This clue is a double definition.
'comparatively shrewd' is the first definition.
(arch can mean knowing or shrewd)
'one that might have quarrel' is the second definition.
(quarrel is a type of arrow)
(Other definitions for archer that I've seen before include "Toxophilite" , "Bow and arrow user" , "One uses bows and arrows" , "launcher of projectile" , "A bow-and-arrow man" .)