Completely exhausted but making maximum effort (3,3)
I believe the answer is:
all out
'completely' is the definition.
(thesaurus)
'exhausted but making maximum effort' is the wordplay.
I cannot quite understand how this works, but
'exhausted' could be 'out' (I've seen this in other clues) and 'out' is located in the answer.
'maximum effort' could be 'all' (I've seen this in another clue) and 'all' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for all out that I've seen before include "tenth wicket has been taken" , "Innings closed" , "Putting full effort into" , "Determined" , "total" .)