Expulsion got us in trouble (7)
I believe the answer is:
ousting
'expulsion' is the definition.
(I know that ousting is a type of expulsion)
'got us in trouble' is the wordplay.
'trouble' indicates anagramming the letters.
'got'+'us'+'in'='gotusin'
'gotusin' is an anagram of 'OUSTING'.
(Other definitions for ousting that I've seen before include "Evicting" , "Driving out" , "ejecting" , "Turfing out" .)