Upsetting Bill, a chin swelling (9)
I believe the answer is:
chilblain
'swelling' is the definition.
(thesaurus)
'upsetting bill a chin' is the wordplay.
'upsetting' indicates anagramming the letters.
'bill'+'a'+'chin'='billachin'
'billachin' is an anagram of 'CHILBLAIN'.
(Other definitions for chilblain that I've seen before include "Inflammation from exposure to cold and moisture" , "Painful swelling on the skin brought on by cold" , "Inflamed sore" , "Painful swelling in winter" , "Painful swelling on hand or foot caused by cold" .)