Falls in war against rising (7)
I believe the answer is:
niagara
'falls' is the definition.
(Niagara Falls)
'in war against rising' is the wordplay.
'in' indicates a hidden word.
'rising' shows that the letters should be reversed in order (in a down clue, letters go up).
'aragain' can be found hidden inside 'war against'.
'aragain' backwards is 'NIAGARA'.
(Other definitions for niagara that I've seen before include "A lot of falling water" , "N. American waterfall" , "it's quite a height" , "& 22 Down North American cascade" , "Horseshoe, American and Bridal Veil Falls, collectively" .)