Horse making the run (6)
I believe the answer is:
hunter
'horse' is the definition.
(I've seen this before)
'making the run' is the wordplay.
'making' indicates anagramming the letters.
'the'+'run'='therun'
'therun' is an anagram of 'HUNTER'.
(Other definitions for hunter that I've seen before include "Orion -- pocket watch with a hinged protective lid" , "one chasing the game?" , "Pursuer of game" , "One chasing - type of watch" , "'Nimrod or Orion, say (6)'" .)