Injured by a hothead with a weapon (6)
I believe the answer is:
harmed
'injured' is the definition.
(harming is a kind of injuring)
'by a hothead with a weapon' is the wordplay.
'by' means one lot of letters go next to another.
'a hothead' becomes 'h' (head letter of 'hot').
'with a weapon' becomes 'armed' (I've seen this before).
'h' put next to 'armed' is 'HARMED'.
(Other definitions for harmed that I've seen before include "Hurt" , "Injured or damaged" .)