Catch horse by entrance to stable (4)
I believe the answer is:
snag
'catch' is the definition.
(snagging is a kind of catching)
'horse by entrance to stable' is the wordplay.
'horse' becomes 'nag' (nag is a kind of horse).
'by' is a charade indicator (letters next to each other).
'entrance to' indicates taking the first letters.
The initial letter of 'stable' is 's'.
'nag' put after 's' is 'SNAG'.
(Other definitions for snag that I've seen before include "Minor hitch" , "Rip or tear" , "Hitch, obstacle" , "Complication, drawback" , "Difficulty; catch" .)