Kept talking, to fluster the fellow (7,2)
I believe the answer is:
rattled on
'kept talking' is the definition.
(to rattle on is to talk incessantly)
'fluster the fellow' is the wordplay.
'fluster' becomes 'rattle' (I've seen this before).
'the fellow' becomes 'don' (both can mean an academic).
'rattle'+'don'='RATTLED ON'
'to' acts as a link.
(Other definitions for rattled on that I've seen before include "talked at length" , "talked incessantly" .)