Tow-headed cad, a bit of a pig (7)
I believe the answer is:
trotter
'a bit of a pig' is the definition.
('trotter' is part of 'pig')
'tow-headed cad' is the wordplay.
'tow-headed' becomes 't' (this might be a standard abbreviation of which I'm unaware).
'cad' becomes 'rotter' (I've seen this before).
't'+'rotter'='TROTTER'
Can you help me to learn more?
(Other definitions for trotter that I've seen before include "Food for man" , "Harnessed mount" , "Briskly moving horse - pig's foot" , "Edible foot?" , "bit of a pig" .)