Discharge a fellow when attacked (5,2)

I believe the answer is:

fired on

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'attacked' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'discharge a fellow' is the wordplay.
'discharge' becomes 'fire' (synonyms).
'a fellow' becomes 'don' (both can mean an academic).
'fire'+'don'='FIRED ON'

'when' is the link.

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