Hoax by Yankee showman (4)
I believe the answer is:
cody
'showman' is the definition.
(William "Buffalo Bill" Cody)
'hoax by yankee' is the wordplay.
'hoax' becomes 'cod' (I've seen this before**).
'by' means one lot of letters go next to another.
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'cod'+'y'='CODY'
(Other definitions for cody that I've seen before include "Buffalo Bill's surname" , "Surname of Buffalo Bill" .)