Barrier damaged best coal (8)
I believe the answer is:
obstacle
'barrier' is the definition.
(thesaurus)
'damaged best coal' is the wordplay.
'damaged' indicates an anagram.
'best'+'coal'='bestcoal'
'bestcoal' anagrammed gives 'OBSTACLE'.
(Other definitions for obstacle that I've seen before include "Thing blocking progress" , "Hurdle, impediment" , "Stab Cleo (anag) - which hinders progress" , "bar" , "stumbling block" .)