Cut one blood-drenched knight (6)
I believe the answer is:
ignore
'cut' is the definition.
(cut can mean to ignore socially)
'one blood-drenched knight' is the wordplay.
'one' becomes 'i' (Roman numeral).
'blood' becomes 'gore' (gore means blood or violence).
'drenched' is an insertion indicator.
'knight' becomes 'N' (chess abbreviation).
'gore' going around 'n' is 'gnore'.
'i'+'gnore'='IGNORE'
(Other definitions for ignore that I've seen before include "Spurn" , "Slight" , "Pay no heed to" , "Region (anag)" , "Neglect" .)