Renounce somewhat degenerate backing (6)
I believe the answer is:
renege
'renounce' is the definition.
(I've seen this before)
'somewhat degenerate backing' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'backing' is a reversal indicator.
'egener' can be found hidden inside 'degenerate'.
'egener' back-to-front is 'RENEGE'.
(Other definitions for renege that I've seen before include "Fail to follow suit at cards" , "Fail to honour an obligation" , "South American cowboy" , "In card games, revoke" , "Fail to fulfil a promise or obligation" .)