Everyone in competition for conscription (4-2)
I believe the answer is:
call-up
'conscription' is the definition.
(I've seen this before)
'everyone in competition' is the wordplay.
'everyone' becomes 'all' (all people).
'in' is an insertion indicator.
'competition' becomes 'cup' (eg the FA Cup).
'all' put into 'cup' is 'CALL-UP'.
'for' is the link.
(Other definitions for call-up that I've seen before include "Conscription" , "Summons to serve in the armed forces" .)