Don't follow through (6)
I believe the answer is:
renege
'don't follow through' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for renege that I've seen before include "Default" , "Go back (on promise etc)" , "Fail to keep promise, or revoke in cards" , "Fail to follow suit at cards" , "Go back on an obligation" .)