Get rid of knightly combat as Jack leaves (4)
I believe the answer is:
oust
'get rid of' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for oust that I've seen before include "Put out, say of office" , "Throw out" , "Unseat" , "Extract" , "Give marching orders" .)