Joint liability established by court appearances? (6,5)
I believe the answer is:
tennis elbow
'joint liability' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'court appearances?' is the wordplay.
'court' becomes 'tennis court' (tennis court is a kind of court).
'appearances?' becomes 'elbow' (I can't justify this - if you can you should give a lot more credence to this answer).
'tennis'+'elbow'='TENNIS-ELBOW'
'established by' is the link.
Can you help me to learn more?
(Other definitions for tennis elbow that I've seen before include "Tendon problem" , "problem for person serving" , "Inflammation of an arm tendon" , "Muscular injury from exercise" , "Joint inflammation" .)