Hitch a horse to a pole (4)
I believe the answer is:
snag
'hitch' is the definition.
(I know that hitch can be written as snag)
'a horse to a pole' is the wordplay.
'a horse' becomes 'nag' (term for an old horse).
'to a' says to put letters next to each other (I've seen this in other clues).
'pole' becomes 's' (abbreviation for South, as in South Pole).
'nag' put after 's' is 'SNAG'.
(Other definitions for snag that I've seen before include "Jag" , "A hidden or unexpected obstacle" , "Tear - catch" , "Unexpected difficulty" , "Stumbling block" .)