Legal arguments shortened festival (4)
I believe the answer is:
gala
'festival' is the definition.
(I've seen this before)
'legal arguments shortened' is the wordplay.
'shortened' says the answer is hidden in the clue (a shortened or reduced extract from the clue).
'GALA' is hidden within 'legal arguments'.
(Other definitions for gala that I've seen before include "Festive entertainment" , "Jamboree" , "Prod with the elbow" , "Festive performance" , "Special sports event" .)