Writer’s material recalled stuff for one reflecting critical situation (5-4)
I believe the answer is:
knife-edge
'critical situation' is the definition.
(I've seen this before)
'writer's material recalled stuff for one reflecting' is the wordplay.
'writer's material' becomes 'ink' (I've seen this in other clues).
'recalled' shows that the letters should be reversed in order.
'stuff' becomes 'feed' (I can't explain this - if you can you should give a lot more credence to this answer).
'for one' becomes 'eg' (both can mean 'for example').
'reflecting' is a reversal indicator.
'ink' reversed gives 'kni'.
'eg' back-to-front is 'ge'.
'kni'+'feed'+'ge'='KNIFE-EDGE'
Can you help me to learn more?
(Another definition for knife-edge that I've seen is " precarious situation".)