Legendary ruler's blood on courtyard by ancient city (4,6)
I believe the answer is:
king arthur
'legendary ruler's' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'blood on courtyard by ancient city' is the wordplay.
'blood' becomes 'kin' (both can mean one's family).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'courtyard' becomes 'garth' (type of open space).
'by' means one lot of letters go next to another.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'kin'+'garth'+'ur'='KING ARTHUR'
Can you help me to learn more?
(Other definitions for king arthur that I've seen before include "Legendary monarch" , "Guinevere's husband" .)