Extravagant fellow pegs out in a reaping machine (3,7)
I believe the answer is:
'extravagant fellow' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'pegs out in a reaping machine' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'in' indicates putting letters inside.
'a reaping machine' becomes 'binder' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pegs' anagrammed gives 'gspe'.
'gspe' inserted into 'binder' is 'BIG SPENDER'.
Can you help me to learn more?
(Another definition for big spender that I've seen is " prodigal type?".)