Trials take place here shortly — one has to be still (8)
I believe the answer is:
inactive
'still' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for inactive that I've seen before include "Passive, not working or in motion" , "Immobile, not working" , "Not moving/working" , "Still" , "Passive, doing nothing" .)