Fellow score badly in wall painting? (6)
I believe the answer is:
'wall painting?' is the definition.
(fresco is a kind of wall painting)
'fellow score badly in' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'badly' is an anagram indicator.
'in' indicates putting letters inside.
'score' is an anagram of 'resco'.
'f' placed inside 'resco' is 'FRESCO'.
(Other definitions for fresco that I've seen before include "Painting using watercolours on plaster", "Mural painted on a wall", "Work of art", "Mural painted on wet plaster", "Artistic work".)