Writer’s rating limiting University centre (3)
I believe the answer is:
hub
'centre' is the definition.
(hub is a kind of centre)
'writer's rating limiting university' is the wordplay.
'writer's rating' becomes 'hb' (HB is a 'hard black' rating on a pencil).
'limiting' is an insertion indicator.
'university' becomes 'u' (abbreviation for university).
'hb' placed around 'u' is 'HUB'.
(Other definitions for hub that I've seen before include "Centre of activity" , "Centre of wheel" , "Centre (of network)" , "Wheel's centre" , "Focal point of activity" .)