Able Scot's tricky snag... (8)
I believe the answer is:
obstacle
'snag' is the definition.
(thesaurus)
'able scot's tricky' is the wordplay.
'tricky' indicates an anagram.
'able'+'scot'='ablescot'
'ablescot' is an anagram of 'OBSTACLE'.
(Other definitions for obstacle that I've seen before include "Blockage, hindrance" , "It obstructs or hinders" , "Progress blocker" , "Block to progress" , "stumbling block" .)