Backing over University square (4)
I believe the answer is:
four
'square' is the definition.
(four is a square number)
'backing over university' is the wordplay.
'backing' becomes 'for' (I've seen this in another clue).
'over' is an insertion indicator.
'university' becomes 'U' (abbreviation for university).
'for' going around 'u' is 'FOUR'.
(Other definitions for four that I've seen before include "Bridge quorum" , "Figure" , "boat crew" , "Square number" , "How many Horsemen of the Apocalypse?" .)