Part of leg held in cynical foul (4)
I believe the answer is:
calf
'part of leg' is the definition.
('calf' is part of 'leg')
'held in cynical foul' is the wordplay.
'held in' indicates the answer is hidden within the clue.
'CALF' is hidden in the letters of 'cynical foul'.
(Other definitions for calf that I've seen before include "beef" , "Young of domestic cattle" , "Fine leather - young whale" , "Young cow - part of the leg" , "Roo's mum (A. A. Milne)" .)