Sprinted to catch old horse (4)
I believe the answer is:
roan
'horse' is the definition.
(I know that roan is a type of horse)
'sprinted to catch old' is the wordplay.
'sprinted' becomes 'ran' (I've seen this in another clue).
'to catch' is an insertion indicator.
'old' becomes 'o' (abbreviation).
'ran' placed around 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "Horse with a coat of mixed colour" , "Nora (anag) - horse" , "Red-coloured horse" , "Bay horse with white/grey hairs in its coat" , "nag" .)