Beat down the old woman with the bad leg (6)
I believe the answer is:
haggle
'beat down' is the definition.
(thesaurus)
'the old woman with the bad leg' is the wordplay.
'the old woman' becomes 'hag' (hag is a kind of old woman).
'with' means one lot of letters go next to another.
'the bad' is an anagram indicator.
'leg' is an anagram of 'gle'.
'hag'+'gle'='HAGGLE'
(Other definitions for haggle that I've seen before include "Fetter (horse's) legs" , "Bargain hard" , "Negotiate the price" , "Bargain over price" , "Argue about price while bargaining" .)