Tango with cad, bit of a pig (7)
I believe the answer is:
trotter
'bit of a pig' is the definition.
('trotter' is part of 'pig')
'tango with cad' is the wordplay.
'tango' becomes 'T' (phonetic alphabet: alpha, bravo, charlie etc.).
'with' says to put letters next to each other.
'cad' becomes 'rotter' (I've seen this in another clue).
't'+'rotter'='TROTTER'
(Other definitions for trotter that I've seen before include "horse getting sulky, say" , "foot of animal for food" , "A slow runner or a pig's foot" , "Pig's foot - type of racing horse" , "Briskly moving horse - pig's foot" .)