Bar by college in Oblates' complex (8)
I believe the answer is:
obstacle
'bar' is the definition.
(thesaurus)
'college in oblates' complex' is the wordplay.
'college' becomes 'c'.
'in' is an insertion indicator.
'complex' indicates anagramming the letters.
'oblates' anagrammed gives 'obstale'.
'c' going inside 'obstale' is 'OBSTACLE'.
'by' acts as a link.
(Other definitions for obstacle that I've seen before include "A spanner in the works?" , "race" , "It obstructs or hinders" , "Barrier or deterrent" , "Maybe let" .)