I lead in Polish part of leg (7)
I believe the answer is:
hipbone
'part of leg' is the definition.
(I know that hipbone is part of leg)
'i lead in polish' is the wordplay.
'lead' becomes 'Pb' (Pb is the chemical symbol for lead).
'in' is an insertion indicator.
'polish' becomes 'hone' (I've seen this in another clue).
'i'+'pb'='ipb'
'ipb' placed within 'hone' is 'HIPBONE'.
(Other definitions for hipbone that I've seen before include "bit of leg" , "One half of the pelvis" , "Large part of skeleton" .)