A surprisingly mature ham? (7)
I believe the answer is:
amateur
'ham?' is the definition.
(I've seen this before)
'a surprisingly mature' is the wordplay.
'surprisingly' indicates anagramming the letters (a surprising ordering of the letters).
'mature' anagrammed gives 'mateur'.
'a'+'mateur'='AMATEUR'
(Other definitions for amateur that I've seen before include "Of sportsman, not professional" , "Unpaid practitioner" , "Receiving no money" , "Inexpert" , "Unprofessional" .)