Knife fight pinching cash box, practically (8)
I believe the answer is:
stiletto
'knife' is the definition.
(stiletto is a kind of knife)
'fight pinching cash box practically' is the wordplay.
'fight' becomes 'setto' (set-to is a kind of fight).
'pinching' indicates putting letters inside (taking inside).
'cash box' becomes 'till'.
'practically' means to remove the last letter.
'till' with its final letter taken away is 'til'.
'setto' placed around 'til' is 'STILETTO'.
(Other definitions for stiletto that I've seen before include "Tapering dagger" , "dangerous weapon" , "Sort of knife" , "Long dagger" , "Thin dagger; heel" .)