Staff covering grass before hot old race (8)
I believe the answer is:
marathon
'race' is the definition.
(thesaurus)
'staff covering grass before hot old' is the wordplay.
'staff' becomes 'man' (manning is a kind of staffing).
'covering' indicates putting letters inside.
'grass' becomes 'rat' (I've seen this before).
'before hot old' becomes 'ho' (I can't justify this - if you can you should believe this answer much more).
'rat'+'ho'='ratho'
'man' going around 'ratho' is 'MARATHON'.
Can you help me to learn more?
(Other definitions for marathon that I've seen before include "26-mile foot race" , "Severe test of endurance" , "Race; battle" , "no easy task" , "Roman hat (anag) - race" .)