The most common and most likely answer to this crossword clue is the 1 plus 2 plus 3 plus 8 letter word I AM THE GREATEST
I
A
M
T
H
E
G
R
E
A
T
E
S
T
Buddy explains!
The straight part
We know that "him/What 8 19 would shout" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case him/what 8 19 would shout = i am the greatest.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.