Traitor I cast, after queen (8)
I believe the answer is:
quisling
'traitor' is the definition.
(I know that Quisling is a type of traitor)
'i cast after queen' is the wordplay.
'cast' becomes 'sling' (slinging is a kind of casting).
'after' says to put letters next to each other.
'queen' becomes 'qu' (abbreviation for queen).
'i'+'sling'='isling'
'isling' after 'qu' is 'QUISLING'.
(Other definitions for quisling that I've seen before include "(Norwegian) WWII collaborator" , "Wartime collaborator" , "Traitor to country, after proNazi Norwegian" , "Judas?" , "Collaborator with an occupying force" .)