Line taken by a king that was shot at Agincourt (5)
I believe the answer is:
arrow
'that was shot at agincourt' is the definition.
(arrows were fired during the Battle of Agincourt)
'line taken by a king' is the wordplay.
'line' becomes 'row' (row is a kind of line).
'taken by' is a charade indicator (letters next to each other).
'a king' becomes 'ar' (I've seen this in other clues).
'row' put after 'ar' is 'ARROW'.
(Other definitions for arrow that I've seen before include "One in a quiver" , "Archer's missile" , "production of Fletcher?" , "Missile of the archer" , "What's shot from a bow" .)