Fight off backward attitude to a once ostracised person (5)
I believe the answer is:
repel
'fight off' is the definition.
(synonyms)
'backward attitude to a once ostracised person' is the wordplay.
I cannot quite see how this works, but
'person' could be 'rep' (rep is a kind of person) and 'rep' is found within the answer.
The remaining letters 'el' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for repel that I've seen before include "'Drive back, repulse (5)'" , "Drive back like leper" , "Hold off" , "Fight off - drive back" , "Reject" .)