Possible excuse for missing court appearance? (6,5)
I believe the answer is:
tennis elbow
'possible excuse for missing' is the definition.
I can't tell whether this defines the answer.
'court appearance?' is the wordplay.
'court' becomes 'tennis court' (tennis court is a kind of court).
'appearance?' becomes 'elbow' (I am not sure about this - if you are sure you should believe this answer much more).
'tennis'+'elbow'='TENNIS-ELBOW'
(Other definitions for tennis elbow that I've seen before include "Painful condition" , "Joint inflammation" , "problem for person serving" , "Tendon problem" , "Inflammation of an arm tendon" .)