Band involved in aggro, upset (5)
I believe the answer is:
group
'band' is the definition.
(thesaurus)
'involved in aggro upset' is the wordplay.
'involved in' indicates a hidden word.
'GROUP' is hidden within 'aggro upset'.
(Other definitions for group that I've seen before include "Number or people or things classed together" , "Number of associated individuals" , "Aggregation" , "A number of elements with something in common (50" , "Unit of pop performers" .)