Hitch or glitch (4)
I believe the answer is:
snag
I believe this is a double definition.
'hitch' is the first definition.
(I know that hitch can be written as snag)
'glitch' is the second definition.
(I've seen this in another clue)
(Other definitions for snag that I've seen before include "Unexpected difficulty" , "Hidden drawback; tear" , "Sharp protuberance; catch" , "Catch -- problem" , "Hitch, unexpected problem" .)