Fired up in fight, produces a knife (8)
I believe the answer is:
stiletto
'a knife' is the definition.
(stiletto is a kind of knife)
'fired up in fight' is the wordplay.
'fired' becomes 'lit' (set on fire).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'in' indicates putting letters inside.
'fight' becomes 'setto' (set-to is a kind of fight**).
'lit' reversed gives 'til'.
'til' put inside 'setto' is 'STILETTO'.
'produces' acts as a link.
(Other definitions for stiletto that I've seen before include "Kind of heel" , "Item of footwear" , "Thin blade" , "One may have a stab" , "part of boot?" .)