Strangely hesitant to accept American supporter (10)
I believe the answer is:
enthusiast
'supporter' is the definition.
(I've seen this before)
'strangely hesitant to accept american' is the wordplay.
'strangely' is an anagram indicator.
'to accept' means one lot of letters goes inside another.
'american' becomes 'us'.
'hesitant' anagrammed gives 'enthiast'.
'enthiast' placed around 'us' is 'ENTHUSIAST'.
(Other definitions for enthusiast that I've seen before include "One deeply interested in a subject" , "Devotee" , "Fan" , "Ardent supporter" , "one not at all cool" .)