Shout, “Elbow is bent around middle of niblick” (6)
I believe the answer is:
bellow
'shout' is the definition.
(bellow is a kind of shout)
'elbow is bent around middle of niblick' is the wordplay.
'is bent' is an anagram indicator.
'around' is an insertion indicator.
'middle of' means to look at the middle letters.
The central letter of 'niblick' is 'l'.
'elbow' anagrammed gives 'below'.
'below' placed around 'l' is 'BELLOW'.
(Other definitions for bellow that I've seen before include "Shout; Saul --, novelist" , "Roar, shout" , "Roar like a bull" , "author" , "Loud deep sound as by bull" .)