Damage caused by hothead with a weapon (4)
I believe the answer is:
harm
'damage' is the definition.
(I know that damage can be written as harm)
'hothead with a weapon' is the wordplay.
'hothead' becomes 'h' (head letter of 'hot').
'with' means one lot of letters go next to another.
'a weapon' becomes 'arm' (synonyms).
'h'+'arm'='HARM'
'caused by' acts as a link.
(Other definitions for harm that I've seen before include "See 13" , "Hurt, maim" , "Hurt, injure" , "Wound" , "Injure or damage" .)