Chapter really upset Scottish historian (7)
I believe the answer is:
carlyle
'scottish historian' is the definition.
(I've seen this before)
'chapter really upset' is the wordplay.
'chapter' becomes 'c' (**).
'upset' indicates anagramming the letters.
'really' with letters rearranged gives 'arlyle'.
'c'+'arlyle'='CARLYLE'
(Other definitions for carlyle that I've seen before include "Thomas -, Sc. essayist" , "Thomas --, Scottish social historian" , "Victorian historian" , "Scots historian" , "Scottish writer" .)