Old boy's story gripping cold bar (8)
I believe the answer is:
obstacle
'bar' is the definition.
(thesaurus)
'old boy's story gripping cold' is the wordplay.
'old boy's' becomes 'obs' (I've seen this in other clues).
'story' becomes 'tale' ('tale' can be a synonym of 'story').
'gripping' is an insertion indicator.
'cold' becomes 'c' (eg on taps).
'tale' going around 'c' is 'tacle'.
'obs'+'tacle'='OBSTACLE'
(Other definitions for obstacle that I've seen before include "The problem" , "Progress blocker" , "race" , "stumbling block" , "Block to progress" .)