Left-winger beginning to talk rubbish (4)
I believe the answer is:
trot
'left-winger' is the definition.
(I've seen this before)
'beginning to talk rubbish' is the wordplay.
'beginning to' suggests taking the first letters.
'rubbish' becomes 'rot' (I've seen this before).
The first letter of 'talk' is 't'.
't'+'rot'='TROT'
(Other definitions for trot that I've seen before include "Move briskly" , "Jogging pace" , "Fairly brisk pace" , "Run at moderate pace" , "Move like a horse" .)