Mock leader out of weakness (9)
I believe the answer is:
imitation
'mock' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for imitation that I've seen before include "Forgery" , "Simulated" , "A copy of an authentic item" , "produced by copyist?" , "Bogus" .)