Unrestrained tirade about a politician (7)
I believe the answer is:
rampant
'unrestrained' is the definition.
(I've seen this before)
'tirade about a politician' is the wordplay.
'tirade' becomes 'rant' (both can mean an angry outburst).
'about' means one lot of letters goes inside another.
'politician' becomes 'MP' (Member of Parliament).
'a'+'mp'='amp'
'rant' placed around 'amp' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "Mantrap (anag) - unrestrained" , "Out of control" , "Showing unrestrained growth" , "Unrestrained, flourishing excessively" , "On the rampage" .)