Jurisprudence, note, upheld wrong feature of court in court activity (4,6)
I believe the answer is:
lawn tennis
'court in court activity' is the definition.
'lawn tennis' can be an answer for 'activity' (lawn tennis is a kind of activity). I am not certain of the 'court in court' bit.
'jurisprudence note upheld wrong feature' is the wordplay.
'jurisprudence' becomes 'law' (synonyms).
'note' becomes 'n' (abbreviation).
'upheld' shows that the letters should be reversed in order.
'wrong feature' becomes 'sinnet' (I can't explain this - if you can you should believe this answer much more).
'sinnet' reversed gives 'tennis'.
'law'+'n'+'tennis'='LAWN TENNIS'
'of' is the link.
Can you help me to learn more?
(Other definitions for lawn tennis that I've seen before include "sport" , "Court game" , "Real alternative" , "Wimbledon game" , "court action results" .)