A cry of disgust after new tier becomes more troublesome (9)
I believe the answer is:
naughtier
'more troublesome' is the definition.
'a cry of disgust after new tier' is the wordplay.
'cry of disgust' becomes 'ugh' (expression of disgust).
'after' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'a'+'ugh'='augh'
'augh' put after 'n' is 'naugh'.
'naugh'+'tier'='NAUGHTIER'
'becomes' acts as a link.
(Other definitions for naughtier that I've seen before include "Worse" , "more unruly" , "More badly behaved" , "More mischievous" , "Less well behaved" .)