Northern theatre knight will bully (8)
I believe the answer is:
threaten
'bully' is the definition.
(I've seen this before)
'northern theatre knight' is the wordplay.
I cannot really understand how this works, but
'northern' could be 'n' (abbreviation e.g. N. Ireland) and 'n' is found in the answer.
an anagram of 'theatre' is 'threate' which is located in the answer.
No letters remain.
This explanation may well be incorrect...
'will' is the link.
Can you help me to learn more?
(Other definitions for threaten that I've seen before include "Bully" , "Foreshadow" , "Utter intentions of injury or punishment" , "Impend, portend" , "indicate danger" .)