Resist social outcast turning up (5)
I believe the answer is:
repel
'resist' is the definition.
(thesaurus)
'social outcast turning up' is the wordplay.
'social outcast' becomes 'leper' (someone with leprosy).
'turning up' says the letters should be written backwards.
'leper' written backwards gives 'REPEL'.
(Other definitions for repel that I've seen before include "Be effective in controlling" , "Drive back, rebuff" , "Put off - disgust" , "Parry" , "may turn your stomach" .)