Understanding crowd (9)
I believe the answer is:
gathering
I believe this clue is a double definition.
'understanding' is the first definition.
('gather' can be a synonym of 'understand')
'crowd' is the second definition.
(I've seen this before)
(Other definitions for gathering that I've seen before include "Sewing" , "bee" , "Understanding - crowd" , "Assembly or concentration" , "Assembly; a boil" .)