Hitches a horse in a ship (5)
I believe the answer is:
snags
'hitches' is the definition.
(snagging is a kind of hitching)
'a horse in a ship' is the wordplay.
'a horse' becomes 'nag' (nag is a kind of horse).
'in' indicates putting letters inside.
'a ship' becomes 'ss'.
'nag' placed inside 'ss' is 'SNAGS'.
(Other definitions for snags that I've seen before include "Problems" , "Drawbacks" , "Hitches" , "Unexpected obstacles" , "Unforeseen obstacles" .)