Unexpected hitch (4)
I believe the answer is:
snag
'unexpected hitch' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for snag that I've seen before include "Sang about obstacle" , "Complication, drawback" , "Disadvantage - small hole in fabric" , "Slight problem" , "Hidden obstacle or catch" .)