Fall guy within is too gentle (6)
I believe the answer is:
stooge
'fall guy' is the definition.
(both can mean someone who takes blame)
'within is too gentle' is the wordplay.
'within' says the answer is hidden in the clue.
'STOOGE' can be found hidden inside 'is too gentle'.
(Other definitions for stooge that I've seen before include "A comedian's assistant, butt of his jokes" , "Comedian's sidekick" , "Comedian's assistant-victim" , "comedy partner" , "Performer who is butt of another's jokes" .)