Horse galloped round circle (4)
I believe the answer is:
roan
'horse' is the definition.
(roan is a kind of horse)
'galloped round circle' is the wordplay.
'galloped' becomes 'ran' (I've seen this in other clues).
'round' is an insertion indicator.
'circle' becomes 'o'.
'ran' enclosing 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "Horse with brownish coat speckled with white" , "Red-coloured horse" , "Horse with main colour interspersed with hairs of another" , "Horse with reddish-brown coat" , "Nora (anag) - horse" .)