Stopping packing the cases and turning it on (9)
I believe the answer is:
cessation
'it on' is the definition.
The definition suggests a singular noun which matches the answer.
'stopping packing the cases and turning' is the wordplay.
'stopping' becomes 'tio' (I can't justify this - if you can you should believe this answer much more).
'packing' indicates putting letters inside.
'and' becomes 'n' (common abbreviation for 'and').
'turning' is an anagram indicator.
'cases'+'n'='casesn'
'casesn' anagrammed gives 'cessan'.
'tio' placed inside 'cessan' is 'CESSATION'.
Can you help me to learn more?
(Other definitions for cessation that I've seen before include "Halt" , "An ending of canoeists" , "Canoeists (anag.)" , "Process of stopping" , "Termination" .)