Golf does perhaps upset huge appetite (5)
I believe the answer is:
greed
'huge appetite' is the definition.
'greed' can be an answer for 'appetite' (thesaurus). I'm not sure about the 'huge' bit.
'golf does perhaps upset' is the wordplay.
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'does perhaps' becomes 'deer' (I've seen this in another clue).
'upset' says the letters should be written backwards.
'deer' backwards is 'reed'.
'g'+'reed'='GREED'
Can you help me to learn more?
(Other definitions for greed that I've seen before include "Craving" , "Vice" , "Avidity" , "Avarice, cupidity" , "Immoderate desire" .)