Spots master pocketing note (4)
I believe the answer is:
acne
'spots' is the definition.
(I've seen this before)
'master pocketing note' is the wordplay.
'master' becomes 'ace'.
'pocketing' means one lot of letters goes inside another.
'note' becomes 'n' (abbreviation).
'ace' enclosing 'n' is 'ACNE'.
(Other definitions for acne that I've seen before include "Teenage skin blemish" , "Skin problem, mainly of teenagers" , "Spotty complaint" , "Problem to face in" , "Skin condition associated with pimples" .)