Massive caper briefly following concert (8)
I believe the answer is:
gigantic
'massive' is the definition.
(thesaurus)
'caper briefly following concert' is the wordplay.
'caper' becomes 'antics'.
'briefly' means to remove the last letter.
'following' is a charade indicator (letters next to each other).
'concert' becomes 'gig'.
'antics' with its final letter removed is 'antic'.
'antic' after 'gig' is 'GIGANTIC'.
(Other definitions for gigantic that I've seen before include "Of very great size" , "monster" , "Huge, enormous" , "Exceedingly large" , "Great big" .)