Defect of feet, back and flanks (4,5)

'defect' is the definition.
(to defect can mean to swap sides in a conflict)

'feet back and flanks' is the wordplay.
'feet' becomes 'paws' (paw is a kind of foot).
'back' shows that the letters should be reversed in order.
'and' is a charade indicator (letters next to each other).
'flanks' becomes 'sides'.
'paws' backwards is 'swap'.
'swap'+'sides'='SWAP SIDES'

'of' acts as a link.