Unrestrained tirade involving a politician (7)
I believe the answer is:
rampant
'unrestrained' is the definition.
(thesaurus)
'tirade involving a politician' is the wordplay.
'tirade' becomes 'rant' (I've seen this before).
'involving' is an insertion indicator.
'politician' becomes 'mp'.
'a'+'mp'='amp'
'rant' placed around 'amp' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "Out of control" , "Unbridled" , "Showing unrestrained growth" , "running wild" , "Rife" .)