Had too little endurance, one grasped (10)
I believe the answer is:
understood
'grasped' is the definition.
(I've seen this in another clue)
'had too little endurance one' is the wordplay.
I cannot really understand how this works, but
'had' could be 'd' (in contractions e.g. 'I'd', 'you'd' etc) and 'd' is found within the answer.
'one' could be 'un' (northern English dialect form of 'one') and 'un' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for understood that I've seen before include "Accepted, implied" , "Comprehended" , "Taken as 23 [READ]" , "Got" .)