Leading man appearing in the round (4)
I believe the answer is:
hero
'leading man' is the definition.
(eg the hero of a film)
'in the round' is the wordplay.
'in' indicates the answer is hidden within the clue.
'HERO' is hidden in the letters of 'the round'.
'appearing' acts as a link.
(Other definitions for hero that I've seen before include "Chief good guy in a book or film" , "Man of outstanding courage" , "paragon" , "object of adulation" , "Main protagonist" .)