Crush half of troy weight (7)
I believe the answer is:
trounce
'crush' is the definition.
('trounce' can be a synonym of 'crush')
'half of troy weight' is the wordplay.
'half of' indicates taking half.
'weight' becomes 'ounce' (ounce is a kind of weight**).
'troy' with half the letters taken is 'tr'.
'tr'+'ounce'='TROUNCE'
(Other definitions for trounce that I've seen before include "Wallop" , "Beat heavily" , "Beat resoundingly" , "Utterly defeat" , "Defeat decisively" .)