Some stamina needed for the trial (9,4)
I believe the answer is:
endurance test
'trial' is the definition.
(I have seen 'Trial of stamina' mean 'endurance test' so perhaps 'trial' could also mean 'endurance test')
'some stamina needed for the' is the wordplay.
'some stamina' becomes 'endurance' (I've seen this in another clue).
'needed for' becomes 'tes' (I am not sure about this - if you are sure you should believe this answer much more).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'endurance'+'tes'+'t'='ENDURANCE TEST'
Can you help me to learn more?
(Other definitions for endurance test that I've seen before include "Trial of ability to undergo hardship" , "Trial of stamina" .)