Eccles is upset over American leaving meat in case improper application results (8)
I believe the answer is:
misusage
'case improper application results' is the definition.
The definition suggests a singular noun which matches the answer.
'eccles is upset over american leaving meat in' is the wordplay.
'eccles is' becomes 'I'm' (where the crossword setter is 'Eccles').
'upset over' says the letters should be written in reverse (knocked over).
'american' becomes 'US' (United States).
'leaving meat' becomes 'sage' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'im' written backwards gives 'mi'.
'us' put into 'sage' is 'susage'.
'mi'+'susage'='MISUSAGE'
Can you help me to learn more?
(Other definitions for misusage that I've seen before include "Ill-treatment" , "bad treatment" .)