Not quite having a fit eleven is justifiable (7)
I believe the answer is:
tenable
'justifiable' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tenable that I've seen before include "Late Ben (anag.)" , "okay as regards defence" , "fairly arguable" , "Can be maintained" , "Based on sound reasoning or evidence" .)