The horse trotted round the ring (4)
I believe the answer is:
roan
'the horse' is the definition.
(roan is a kind of horse)
'trotted round the ring' is the wordplay.
'trotted' becomes 'ran' (I've seen this in another clue).
'round' is an insertion indicator.
'the ring' becomes 'o' (letter resembling a ring).
'ran' enclosing 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "Type of 17's coat colouring" , "Of horse, with coat sprinkled with white or grey hairs" , "Horse with reddish-brown coat" , "Horse - leather" , "Bay horse with white/grey hairs in its coat" .)