Fail to follow suit at cards (6)
I believe the answer is:
renege
'fail to follow suit at cards' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for renege that I've seen before include "Withdraw" , "Fail to fulfil a promise or obligation" , "Change one's mind" , "Go back on one's word, break promise" , "Default" .)