Under pressure to answer, perhaps immediately? (2,3,4)
I believe the answer is:
on the spot
I believe this is a double definition.
'under pressure to answer perhaps' is the first definition.
(as in someone put on the spot by a question)
'immediately' is the second definition.
(I've seen this before)
(Other definitions for on the spot that I've seen before include "At the scene of an event, immediately" , "Challenged" , "At the scene of the action" , "At a particular place of action" , "in hot water?" .)