Caught when young soldier briefly falls (7)
I believe the answer is:
cascade
'falls' is the definition.
(synonyms)
'caught when young soldier briefly' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'young soldier' becomes 'cadet' (I've seen this before).
'briefly' means to remove the last letter.
'cadet' with its last letter taken away is 'cade'.
'c'+'as'+'cade'='CASCADE'
(Other definitions for cascade that I've seen before include "Series of small waterfalls" , "Waterfall or deluge" , "Small waterfall or series of them" , "Rush" , "Sudden downpour" .)