Attack with a broken stone? (5)
I believe the answer is:
onset
'attack' is the definition.
(archaic term for a military attack)
'broken stone?' is the wordplay.
'broken' indicates anagramming the letters.
'stone' anagrammed gives 'ONSET'.
'with a' is the link.
(Other definitions for onset that I've seen before include "Start - attack" , "Appearance of" , "Assault; beginning" , "origin" , "Outbreak" .)