Reject or push back outcast (5)
I believe the answer is:
repel
'reject' is the definition.
(I know that repel is a more specific form of reject)
'push back outcast' is the wordplay.
'push back' is a reversal indicator (I've seen 'pushed back' mean this).
'outcast' becomes 'leper' (leper is a kind of outcast).
'leper' reversed gives 'REPEL'.
'or' acts as a link.
(Other definitions for repel that I've seen before include "Reject" , "Deflect" , "Fill with distaste" , "See off" , "Drive or force back" .)