Disgust, as outcast knocked over (5)
I believe the answer is:
repel
'disgust' is the definition.
('repel' can be a synonym of 'disgust')
'outcast knocked over' is the wordplay.
'outcast' becomes 'leper' (leper is a kind of outcast).
'knocked over' says the letters should be written backwards.
'leper' in reverse letter order is 'REPEL'.
'as' acts as a link.
(Other definitions for repel that I've seen before include "Successfully resist" , "Drive back or disgust" , "Be effective in controlling" , "Deflect" , "'Drive back, repulse (5)'" .)