This outcast returns to drive back (5)
I believe the answer is:
leper
'this outcast' is the definition.
(leper is a kind of outcast)
'returns to drive back' is the wordplay.
'returns' says the letters should be written in reverse.
'to drive back' becomes 'repel' ('repel' can be a synonym of 'drive back').
'repel' reversed gives 'LEPER'.
(Other definitions for leper that I've seen before include "Social reject" , "despised person" , "Social outcast" , "sick person" , "Someone shunned" .)