Mass trial arranged for scaremongers (9)
I believe the answer is:
alarmists
'scaremongers' is the definition.
(I've seen this before)
'mass trial arranged' is the wordplay.
'arranged' indicates anagramming the letters.
'mass'+'trial'='masstrial'
'masstrial' with letters rearranged gives 'ALARMISTS'.
'for' acts as a link.
(Other definitions for alarmists that I've seen before include "Scaremongers" , "They arouse people's fears needlessly" , "Such will be inclined to panic" .)