Fell down; caved in (9)
I believe the answer is:
collapsed
I believe this clue is a double definition.
'fell down' is the first definition.
(I've seen this before)
'caved in' is the second definition.
('collapse' can be a synonym of 'cave in')
(Other definitions for collapsed that I've seen before include "Fell apart" , "Cracked up - gave way" , "laid low" , "Gave way, caved in" .)