Humiliate editor to lift average (6)
I believe the answer is:
demean
'humiliate' is the definition.
(I know that demean is a more specific form of the action humiliate)
'editor to lift average' is the wordplay.
'editor' becomes 'ed' (abbreviation).
'to lift' shows that the letters should be reversed in order (in a down clue, letters lift up).
'average' becomes 'mean' (type of average).
'ed' in reverse letter order is 'de'.
'de'+'mean'='DEMEAN'
(Other definitions for demean that I've seen before include "'Put down, degrade (6)'" , "Degrade, humiliate" , "Humble" , "Lower, degrade" , "Lower in dignity or reputation" .)