Sheet a fathead gets oil on (4)
I believe the answer is:
foil
'sheet a fathead' is the definition.
'foil' can be an answer for 'sheet' (thesaurus). I am not certain of the 'a fathead' bit.
'gets oil on' is the wordplay.
'gets' becomes 'f' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters go next to another.
'f'+'oil'='FOIL'
Can you help me to learn more?
(Other definitions for foil that I've seen before include "Thin metal sheet; frustrate" , "Prevent from succeeding" , "Frustrate - sheet - rapier" , "metal used in > sword" , "Prevent the success of; fencing sword" .)