The low fellow has to rage wildly! (6)
I believe the answer is:
toerag
'the low fellow' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'to rage wildly' is the wordplay.
'wildly' indicates an anagram.
'rage' with letters rearranged gives 'erag'.
'to'+'erag'='TOERAG'
'has' is the link.
Can you help me to learn more?
(Other definitions for toerag that I've seen before include "despicable sort" , "Scamp" , "Despicable person (slang)" , "O, great! (anag) -- a worthless fellow" , "Despicable chap" .)