Drop weapons and relieve force to stop constant fury (9)
I believe the answer is:
ceasefire
'drop weapons' is the definition.
'relieve force to stop constant fury' is the wordplay.
'relieve' becomes 'ease' (easing is a kind of relieving).
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'to stop' means one lot of letters goes inside another.
'constant' becomes 'c' (mathematical abbreviation).
'fury' becomes 'ire' (I've seen this before).
'ease'+'f'='easef'
'c'+'ire'='cire'
'easef' inserted into 'cire' is 'CEASEFIRE'.
'and' is the link.
(Other definitions for ceasefire that I've seen before include "Break in fighting" , "Truce" .)