Force almost destroyed? That’s rubbish (7)
I believe the answer is:
flotsam
'rubbish' is the definition.
(flotsam is wreckage from a ship)
'force almost destroyed?' is the wordplay.
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
'destroyed?' indicates an anagram.
'almost' with letters rearranged gives 'lotsam'.
'f'+'lotsam'='FLOTSAM'
'that's' acts as a link.
(Other definitions for flotsam that I've seen before include "Wreckage found floating" , "Vagrants" , "The floating wreckage of a ship" , "Detritus" , "Things found floating from a ship" .)