Clumsy, rocking gait of bull that's lost its head (6)
I believe the answer is:
waddle
'clumsy rocking gait' is the definition.
'bull that's lost its head' is the wordplay.
'bull' becomes 'twaddle' (I've seen this before).
'that's lost its head' means to remove the first letter.
'twaddle' with its first letter taken away is 'WADDLE'.
'of' is the link.
(Other definitions for waddle that I've seen before include "Duck-like walk" , "Walk with clumsily swaying motion" , "Move like a duck" , "Walk duck-fashion" , "Walk swayingly" .)