Unsatisfactory article by lecturer occasionally (3,3,2)
I believe the answer is:
off and on
'occasionally' is the definition.
(I've seen this before)
'unsatisfactory article by lecturer' is the wordplay.
'unsatisfactory' becomes 'off' (similar in meaning).
'article' becomes 'an' (English indefinite article).
'by' says to put letters next to each other.
'lecturer' becomes 'don' (don can mean an academic).
'off'+'an'+'don'='OFF-AND-ON'
(Other definitions for off and on that I've seen before include "the two sides at the Oval are this" , "Switch options" , "switch positions" , "sometimes" , "From time to time" .)