Old Donald could certainly shift around the court! (5)
I believe the answer is:
budge
'court' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for budge that I've seen before include "Shift slightly, or cause to alter position" , "Move however slightly" , "Cause to alter an opinion or stance, shift" , "Make the slightest movement" , "Move reluctantly" .)