The horse galloped out of the ring (4)
I believe the answer is:
roan
'the horse' is the definition.
(roan is a kind of horse)
'galloped out of the ring' is the wordplay.
'galloped' becomes 'ran' (I've seen this in other clues).
'out of' is an insertion indicator.
'the ring' becomes 'o'.
'ran' placed around 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "Horse with main colour interspersed with hairs of another" , "Type of 17's coat colouring" , "Horse - leather" , "Horse with a coat of mixed colour" , "Nora (anag) - horse" .)