Soldier is impetuous, turning up to entertain us (6)
I believe the answer is:
hussar
'soldier' is the definition.
(hussar is a kind of soldier)
'impetuous turning up to entertain us' is the wordplay.
'impetuous' becomes 'rash' (I've seen this before).
'turning up' says the letters should be written backwards.
'to entertain' is an insertion indicator.
'rash' in reverse letter order is 'hsar'.
'hsar' going around 'us' is 'HUSSAR'.
'is' is the link.
(Other definitions for hussar that I've seen before include "Soldier in a light cavalry regiment" , "Member of a light cavalry regiment" , "one often up on a charge" , "Hungarian soldier" , "Cavalryman, originally Hungarian" .)