Spar's closed after class (3-2)
I believe the answer is:
set-to
'spar's' is the definition.
(thesaurus)
'closed after class' is the wordplay.
'closed' becomes 'to' (as in a door closed to).
'after' is a charade indicator (letters next to each other).
'class' becomes 'set' (I've seen this before).
'to' put after 'set' is 'SET-TO'.
(Other definitions for set-to that I've seen before include "Fight, argument" , "Scrap" , "Altercation" , "brush with violence?" , "Ready - fight" .)