Leaving contentious point on painful condition (6,3)

I believe the answer is:

opting out

'leaving' is the definition.
(eg to opt out of a scheme is to leave it)

'contentious point on painful condition' is the wordplay.
'contentious' indicates anagramming the letters (a contentious or difficult version of the letters).
'on' is a charade indicator (letters next to each other).
'painful condition' becomes 'gout'.
'point' with letters rearranged gives 'optin'.
'optin'+'gout'='OPTING OUT'

I've seen this clue in The Guardian.

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