Or backing politician in frolic (4)
I believe the answer is:
romp
'frolic' is the definition.
(I know that frolic can be written as romp)
'or backing politician' is the wordplay.
'backing' says the letters should be written backwards.
'politician' becomes 'MP' (Member of Parliament).
'or' written backwards gives 'ro'.
'ro'+'mp'='ROMP'
'in' is the link.
(Other definitions for romp that I've seen before include "Boisterous party" , "light-hearted outing" , "Make merry at prom" , "Easy victory; play around energetically" , "Boisterous prank" .)