Embarrassed, steal back to the frontier (6)
I believe the answer is:
border
'the frontier' is the definition.
(I've seen this in another clue)
'embarrassed steal back' is the wordplay.
'embarrassed' becomes 'red' (someone may blush or go red when embarrassed).
'steal' becomes 'rob' (robbing is a kind of stealing).
'back' says the letters should be written in reverse.
'red'+'rob'='redrob'
'redrob' reversed gives 'BORDER'.
'to' acts as a link.
(Other definitions for border that I've seen before include "An edgy place" , "Edge or boundary" , "BLINK/BRINK" , "Line between countries" , "Margin along the edge" .)