List of protagonists (4)
I believe the answer is:
rota
'list' is the definition.
(rota is a kind of list)
'of protagonists?' is the wordplay.
'of' indicates a hidden word.
'ROTA' can be found hidden inside 'protagonists'.
(Other definitions for rota that I've seen before include "Cycle of duty" , "Task list, roster" , "List of duties taken in turn" , "List of people to do job in turns" , "Register of names for duties" .)