Blade glowing when lifted in fight (8)
I believe the answer is:
stiletto
'blade' is the definition.
(I have seen 'Thin blade ' mean 'stiletto' so perhaps 'blade' could also mean 'stiletto')
'glowing when lifted in fight' is the wordplay.
'glowing' becomes 'lit' (I've seen this in another clue).
'when lifted' is a reversal indicator (in a down clue, letters go up).
'in' indicates putting letters inside.
'fight' becomes 'setto' (set-to can mean a fight or argument).
'lit' written backwards gives 'til'.
'til' inserted within 'setto' is 'STILETTO'.
(Other definitions for stiletto that I've seen before include "Bedspread" , "Long dagger" , "Thin blade" , "One may have a stab" , "Small dagger and high narrow heel" .)