Man impressed to have left sport, quiet epic hero (9)
I believe the answer is:
gilgamesh
'epic hero' is the definition.
(hero of The Epic of Gilgamesh)
'man impressed to have left sport quiet' is the wordplay.
'man impressed' becomes 'gi' (term for someone impressed into the US army).
'to have' is a charade indicator (letters next to each other).
'left' becomes 'l' (common abbreviation).
'sport' becomes 'game' (I've seen this before**).
'quiet' becomes 'sh'.
'gi'+'l'+'game'+'sh'='GILGAMESH'
(Other definitions for gilgamesh that I've seen before include "1 28 [EPIC POEM]" , "epic character?" .)