Fighter shot arrow, possessing boundless grit (7)
I believe the answer is:
warrior
'fighter' is the definition.
(I've seen this before)
'shot arrow possessing boundless grit' is the wordplay.
'shot' is an anagram indicator.
'possessing' means one lot of letters goes inside another.
'boundless' says to take the centre.
The middle of 'grit' is 'ri'.
'arrow' is an anagram of 'waror'.
'waror' placed around 'ri' is 'WARRIOR'.
(Other definitions for warrior that I've seen before include "Skilled, battle-hardened fighter" , "Brave fighter" , "A man mighty in battle" , "A famous fighter, noble in battle" , "Person engaged in battle" .)