Skill on range? Evaluates staff with it (12)
I believe the answer is:
marksmanship
'skill on range?' is the definition.
'evaluates staff with it' is the wordplay.
'evaluates' becomes 'marks' (marking is a kind of evaluating).
'staff' becomes 'man' (manning is a kind of staffing).
'with it' becomes 'ship' (I can't explain this - if you can you should believe this answer much more).
'marks'+'man'+'ship'='MARKSMANSHIP'
(Other definitions for marksmanship that I've seen before include "Skill with rifle, crossbow etc" , "that needs a keen eye" , "goal-scoring skill" , "Skill in shooting" , "Skill in hitting a target" .)