Intrepid Sally on a fun helter-skelter (8)
I believe the answer is:
unafraid
'intrepid' is the definition.
(I've seen this before)
'sally on a fun helter-skelter' is the wordplay.
'sally' becomes 'raid' (both can mean a military attack).
'on' is a charade indicator (letters next to each other).
'helter skelter' is an anagram indicator.
'a'+'fun'='afun'
'afun' is an anagram of 'unaf'.
'raid' put after 'unaf' is 'UNAFRAID'.
(Other definitions for unafraid that I've seen before include "Not frightened" , "not daunted" , "Courageous" , "showing no fear" , "Not fearful or scared" .)