Hale booming out ... "Blood protein!!" (11)
I believe the answer is:
haemoglobin
'blood protein' is the definition.
'haemoglobin' can be an answer for 'protein' (haemoglobin is a kind of protein). I'm unsure of the 'blood' bit.
'hale booming out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'hale'+'booming'='halebooming'
'halebooming' anagrammed gives 'HAEMOGLOBIN'.
Can you help me to learn more?
(Other definitions for haemoglobin that I've seen before include "Oxygen-carrier in blood" , "Red oxygen-carrying protein in blood cells" .)