Informed group is disturbed (5)
I believe the answer is:
upset
'is disturbed' is the definition.
(synonyms)
'informed group' is the wordplay.
'informed' becomes 'up' (being up on a topic means being informed about it).
'group' becomes 'set' (both can mean a collection).
'up'+'set'='UPSET'
(Other definitions for upset that I've seen before include "Caused grief" , "bug" , "Indisposition" , "Surprise win" , "Disturb - spoil" .)