Resist outcast from the east (5)
I believe the answer is:
repel
'resist' is the definition.
(thesaurus)
'outcast from the east' is the wordplay.
'outcast' becomes 'leper' (leper is a kind of outcast).
'from the east' says the letters should be written backwards.
'leper' written backwards gives 'REPEL'.
(Other definitions for repel that I've seen before include "Parry" , "Sicken" , "Be effective in controlling" , "Turn away" , "Spurn" .)