Send into exile (6)
'send into exile' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for banish that I've seen before include "'Cast out, ostracise (6)'" , "outlaw" , "Send away (as punishment)" , "Expel or expatriate" , "Expel from a community or group" .)
(Other definitions for relegate that I've seen before include "Move down to a lower grade" , "Move to a lower division" , "Assign to a lower position" , "Move to a lower position" , "Downgrade" .)