University can upset this group (4)
I believe the answer is:
unit
'this group' is the definition.
(unit is a kind of group)
'university can upset' is the wordplay.
'university' becomes 'u'.
'can' becomes 'tin' ('tin' can be a synonym of 'can').
'upset' is a reversal indicator.
'tin' reversed gives 'nit'.
'u'+'nit'='UNIT'
(Other definitions for unit that I've seen before include "Single manufactured item; military grouping" , "One; military group" , "hospital department" , "A single, complete item" , "Module" .)