Able Scot moving barrier (8)
I believe the answer is:
obstacle
'barrier' is the definition.
(I know that obstacle is a type of barrier)
'able scot moving' is the wordplay.
'moving' is an anagram indicator (letters are moved around).
'able'+'scot'='ablescot'
'ablescot' anagrammed gives 'OBSTACLE'.
(Other definitions for obstacle that I've seen before include "Hindrance, obstruction" , "Stab Cleo (anag) - which hinders progress" , "It obstructs or hinders" , "race" , "It hinders or prevents advance" .)