The horse ran around with a duck! (4)
I believe the answer is:
roan
'the horse' is the definition.
(roan is a kind of horse)
'ran around with a duck' is the wordplay.
'around with' indicates anagramming the letters.
'a duck' becomes 'o' (resembles zero - 'duck' in cricket).
'ran' anagrammed with 'o' gives 'ROAN'.
(Other definitions for roan that I've seen before include "Two-colour horse" , "Horse with main colour interspersed with hairs of another" , "Horse with reddish-brown coat" , "Bay horse with white/grey hairs in its coat" , "Horse - leather" .)