Tumbled (8)
'tumbled' is the definition.
(to tumble is to fall over)
This is the entire clue.
(Other definitions for fell that I've seen before include "Dropped to the ground" , "Knock down - came down" , "was deflating" , "stretch of moorland" , "Toppled" .)
(Other definitions for rolled that I've seen before include "Rotated" , "Moved along on wheels" , "Furled" .)
(Another definition for cascaded that I've seen is " Poured downwards as a waterfall".)