Trouble? It’s brought in a crowd (7)
I believe the answer is:
agitate
'trouble?' is the definition.
(agitating is a kind of troubling)
'it's brought in a crowd' is the wordplay.
'it's' becomes 'it' (I've seen this in other clues).
'brought in' is an insertion indicator.
'crowd' becomes 'gate' (gate can refer to the crowd for a sporting event).
'a'+'gate'='agate'
'it' inserted inside 'agate' is 'AGITATE'.
(Other definitions for agitate that I've seen before include "Make nervous; stir" , "Get upset" , "Stir violently" , "Make troubled or nervous" , "Upset, disturb the surface of" .)