Calm and collected when American returned blushing (7)
I believe the answer is:
assured
'calm and collected' is the definition.
'when american returned blushing' is the wordplay.
'when' becomes 'as'.
'american' becomes 'us'.
'returned' is a reversal indicator.
'blushing' becomes 'red' (I've seen this before).
'us' back-to-front is 'su'.
'as'+'su'+'red'='ASSURED'
(Other definitions for assured that I've seen before include "Exhibiting confidence" , "Confident and self-possessed" , "Beyond doubt" , "Confident - certain" , "without doubt" .)