Foul - a cleaving chop - the pits (7)
I believe the answer is:
axillae
'the pits' is the definition.
(axilla is the medical name for the armpit)
'foul a cleaving chop' is the wordplay.
'foul' becomes 'ill'.
'cleaving' means one lot of letters goes inside another (inserted letters cleave or split the word).
'chop' becomes 'axe' (axing is a kind of chopping).
'ill'+'a'='illa'
'illa' inserted within 'axe' is 'AXILLAE'.
(Other definitions for axillae that I've seen before include "armpits" , "parts of body" , "sweating there?" .)